engine : Fix CTOR in StorageDomainCommandBase

StorageDomainCommandBase constructor does not pass
CommandContext to super class.

Change-Id: Ib7df161c6d5c112b9bb76ee8b43fbf6f70f37645
Bug-Url: https://bugzilla.redhat.com/1114092
Signed-off-by: Ravi Nori <rnori@redhat.com>