Reduce console noise coming from unit tests:

A few unit tests have historically generated a lot of noise
to the console from log writes.  This noise was not useful
and made it harder to locate actual test failures.

By changing the log level of these tests from
- severities::kError to
- severities::kDisabled
it was possible to remove that noise coming from the logs.

src/test/app/LedgerReplay_test.cpp

@@ -465,7 +465,7 @@ struct LedgerServer
         assert(param.initLedgers > 0);
         createAccounts(param.initAccounts);
         createLedgerHistory();
-        app.logs().threshold(beast::severities::Severity::kWarning);
+        app.logs().threshold(beast::severities::kWarning);
     }
 
     /**
@@ -567,7 +567,10 @@ public:
         PeerSetBehavior behavior = PeerSetBehavior::Good,
         InboundLedgersBehavior inboundBhvr = InboundLedgersBehavior::Good,
         PeerFeature peerFeature = PeerFeature::LedgerReplayEnabled)
-        : env(suite, jtx::envconfig(jtx::port_increment, 3))
+        : env(suite,
+              jtx::envconfig(jtx::port_increment, 3),
+              nullptr,
+              beast::severities::kDisabled)
         , app(env.app())
         , ledgerMaster(env.app().getLedgerMaster())
         , inboundLedgers(