Bug 6710 - Close ClusterSingletonServiceRegistration fix

Note: Closing process for CSSRegistration has to follow same
way as a lostLeadership and the main diferences between this
two ways is a not null MainEntityCandidate registration.

* fix using closeClusterSingletonGroup method
  - this method has to be use ONLY without active EOS listener
* fix closeResources method
  - MainEntityCandidate has to be close before lock.release
* fix removing actual CSSGroup instance from EOS listener map
  - close proces has to always finish with removing parth and
    we have to check guardEntityCandidate instece only. Because
    we don't get any aditional notif. from Eos without
    GuardEntityCandidate registration.
* add and modify test
* add async Test Case for SingletonServiceGroup

Change-Id: I15f89cbd43310b0a8e4b7ac78595eeaaa82a65ee
Signed-off-by: Vaclav Demcak <vdemcak@cisco.com>