This commit:
- modifies GetMonsAndClusterID() to take clusterID instead of options.
- moves out validation of clusterID is set or not out of GetMonsAndClusterID().
- defines ErrClusterIDNotSet new error for reusability.
- add GetClusterID() to obtain clusterID from options.
Signed-off-by: Rakshith R <rar@redhat.com>