Added isActive check to the StandardControllerServiceNode:280 to ensure that
the IF statement can only have a chance to succeed if service is active. The service
will be indiscriminately deactivated as soon as disable(..) operation is invoked. This itself will
eliminate the race condition discovered by Mark
NIFI-1164 addressed PR comments
fixed the race condition described by Mark during disable call
NIFI-1164 polished javadoc
0d09054d9f