Consistently log CValidationState on failure

Seems providing at least minimal visibility to the failure is a good practice.

The only remaining ignored state is in LoadExternalBlockFile, where logging
would likely be spammy.

src/test/test_bitcoin.cpp

@@ -85,7 +85,7 @@ TestingSetup::TestingSetup(const std::string& chainName) : BasicTestingSetup(cha
         {
             CValidationState state;
             if (!ActivateBestChain(state, chainparams)) {
-                throw std::runtime_error("ActivateBestChain failed.");
+                throw std::runtime_error(strprintf("ActivateBestChain failed. (%s)", FormatStateMessage(state)));
             }
         }
         nScriptCheckThreads = 3;