engine: Fix coverity complaints

CID 1223216 (#1 of 1): Using invalid iterator (INVALIDATE_ITERATOR)
 invalid_loop: Attempting to obtain another element from cmdCallBackMap.keySet()
 after it's been modified

Change-Id: I5a80932a9ac16c08fac9faa290f844f22b2f0825
Signed-off-by: Moti Asayag <masayag@redhat.com>