Add missing override keyword:

* Enable the `suggest-override` warning for gcc
* Fix all functions that were flagged by that warning

src/test/rpc/AccountCurrencies_test.cpp

@@ -184,7 +184,7 @@ class AccountCurrencies_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testBadInput ();
         testBasic ();

src/test/rpc/AccountInfo_test.cpp

@@ -314,7 +314,7 @@ public:
         }
     }
 
-    void run()
+    void run() override
     {
         testErrors();
         testSignerLists();

src/test/rpc/AccountLinesRPC_test.cpp

@@ -863,7 +863,7 @@ public:
         BEAST_EXPECT(linesEnd.isMember(jss::id) && linesEnd[jss::id] == 5);
     }
 
-    void run ()
+    void run () override
     {
         testAccountLines();
         testAccountLineDelete();

src/test/rpc/AccountOffers_test.cpp

@@ -267,7 +267,7 @@ public:
 
     }
 
-    void run()
+    void run() override
     {
         testSequential(true);
         testSequential(false);

src/test/rpc/AccountSet_test.cpp

@@ -438,7 +438,7 @@ public:
         env(fset (alice, asfRequireAuth), ter(tecOWNERS));
     }
 
-    void run()
+    void run() override
     {
         testNullAccountSet();
         testMostFlags();

src/test/rpc/AccountTx_test.cpp

@@ -166,7 +166,7 @@ class AccountTX_test : public beast::unit_test::suite
 
 public:
     void
-    run()
+    run() override
     {
         testParameters();
     }

src/test/rpc/AmendmentBlocked_test.cpp

@@ -157,7 +157,7 @@ class AmendmentBlocked_test : public beast::unit_test::suite
     }
 
 public:
-    void run()
+    void run() override
     {
         testBlockedMethods();
     }

src/test/rpc/DepositAuthorized_test.cpp

@@ -216,7 +216,7 @@ public:
         }
     }
 
-    void run()
+    void run() override
     {
         testValid();
         testErrors();

src/test/rpc/GetCounts_test.cpp

@@ -106,7 +106,7 @@ class GetCounts_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testGetCounts();
     }

src/test/rpc/JSONRPC_test.cpp

@@ -2353,7 +2353,7 @@ public:
         }
     }
 
-    void run ()
+    void run () override
     {
         testBadRpcCommand ();
         testAutoFillFees ();

src/test/rpc/KeyGeneration_test.cpp

@@ -709,7 +709,7 @@ public:
         }
     }
 
-    void run()
+    void run() override
     {
         testKeyType (boost::none, secp256k1_strings);
         testKeyType (std::string("secp256k1"), secp256k1_strings);

src/test/rpc/LedgerClosed_test.cpp

@@ -52,7 +52,7 @@ public:
         BEAST_EXPECT(lc_result[jss::ledger_index] == 3);
     }
 
-    void run()
+    void run() override
     {
         testMonitorRoot();
     }

src/test/rpc/LedgerData_test.cpp

@@ -436,7 +436,7 @@ public:
         }
     }
 
-    void run()
+    void run() override
     {
         testCurrentLedgerToLimits(true);
         testCurrentLedgerToLimits(false);

src/test/rpc/LedgerRPC_test.cpp

@@ -1500,7 +1500,7 @@ class LedgerRPC_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testLedgerRequest();
         testBadInput();

src/test/rpc/LedgerRequestRPC_test.cpp

@@ -291,7 +291,7 @@ public:
 
     }
 
-    void run ()
+    void run () override
     {
         testLedgerRequest();
         testEvolution();

src/test/rpc/NoRippleCheck_test.cpp

@@ -227,7 +227,7 @@ class NoRippleCheck_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testBadInput ();
         for (auto user : {true, false})
@@ -327,7 +327,7 @@ class NoRippleCheckLimits_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         for (auto admin : {true, false})
             testLimits (admin);

src/test/rpc/NoRipple_test.cpp

@@ -208,7 +208,7 @@ public:
         }
     }
 
-    void run ()
+    void run () override
     {
         testSetAndClear();
 

src/test/rpc/OwnerInfo_test.cpp

@@ -201,7 +201,7 @@ class OwnerInfo_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testBadInput ();
         testBasic ();

src/test/rpc/Peers_test.cpp

@@ -85,7 +85,7 @@ class Peers_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testRequest();
     }

src/test/rpc/ServerInfo_test.cpp

@@ -88,7 +88,7 @@ public:
         }
     }
 
-    void run ()
+    void run () override
     {
         testServerInfo ();
     }

src/test/rpc/Status_test.cpp

@@ -83,7 +83,7 @@ private:
     }
 
 public:
-    void run()
+    void run() override
     {
         test_OK ();
         test_error ();
@@ -200,7 +200,7 @@ private:
     }
 
 public:
-    void run()
+    void run() override
     {
         test_OK ();
         test_error ();

src/test/rpc/TransactionEntry_test.cpp

@@ -242,7 +242,7 @@ class TransactionEntry_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testBadInput();
         testRequest();

src/test/rpc/TransactionHistory_test.cpp

@@ -142,7 +142,7 @@ class TransactionHistory_test : public beast::unit_test::suite
     }
 
 public:
-    void run ()
+    void run () override
     {
         testBadInput();
         testRequest();

src/test/rpc/ValidatorRPC_test.cpp

@@ -399,7 +399,7 @@ public:
     }
 
     void
-    run()
+    run() override
     {
         testPrivileges();
         testStaticUNL();