Integration tests: Use zaptest.Logger based testing.TB

Thanks to this the logs:
  - are automatically printed if the test fails.
  - are in pretty consistent format.
  - are annotated by 'member' information of the cluster emitting them.

Side changes:
  - Set propert default got DefaultWarningApplyDuration (used to be '0')
  - Name the members based on their 'place' on the list (as opposed to
'random')

raft/raft.go

@@ -230,7 +230,7 @@ func (c *Config) validate() error {
 	}
 
 	if c.Logger == nil {
-		c.Logger = raftLogger
+		c.Logger = getLogger()
 	}
 
 	if c.ReadOnlyOption == ReadOnlyLeaseBased && !c.CheckQuorum {