Remove unused main thread
For ENG-5588, take a stab at removing the check that is only supposed to run at startup
Merge pull request #1012 from VoltDB/ENG-5588

Eng 5588 Clean up random unused thread and fix issue with leader appointer failover startup checks being applied at runtime
Weaken CurrentTimestamp test to allow for valgrind-scale time lags in TestProcedureAPISuite.
Merge branch 'master' into groovy-procedure