core: fix flow of FC DirectLUN disk creation

StorageDomainCommandBase -> proceedLUNInDb:
prevent connections handling for FCP storage
(FCP storage doesn't utilize connections).

Change-Id: Icf0fbd892b4c8549380b4394c8a4545de1da2343
Bug-Url: https://bugzilla.redhat.com/1065014
Signed-off-by: Daniel Erez <derez@redhat.com>