gluster: fix to remove multiple host when hosts are in maintenance

Add a lock to wait for complete gluster command execution
and release

Change-Id: I0f74af59dc0723eda46ac1b7c53b2a980c49fda4
Signed-off-by: Timothy Asir <tjeyasin@redhat.com>
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1024997
Signed-off-by: Timothy Asir <tjeyasin@redhat.com>