Add missing ClassRule TestSupport

Since the Redis/Rabbit SingleNodeIntegrationTests' startup() method
is changed to be static, we need to apply static @ClassRule to
check the TestSupport rule for Redis/Rabbit availability.

Also, the ShellCommandsTestSuite requires ClassRule as the
AbstractShellIntegrationTest has the RedisTestSupport
Prevent NPE if no db files are present
XD-804 Added integration.support package to dirt and used in AbstractSingleNode...Tests