Enable manual tests in CI:

Fixes: RIPD-1575. Fix argument passing to runner. Allow multiple unit
test selectors to be passed via --unittest argument. Add optional
integer priority value to test suite list. Fix several failing manual
tests. Update CLI usage message to make it clearer.

src/test/protocol/digest_test.cpp

@@ -156,6 +156,6 @@ public:
     }
 };
 
-BEAST_DEFINE_TESTSUITE_MANUAL(digest,ripple_data,ripple);
+BEAST_DEFINE_TESTSUITE_MANUAL_PRIO(digest,ripple_data,ripple,20);
 
 } // ripple