Don't make nova-compute depend on iSCSI

Because not all volume drivers require iSCSI it makes sense to not
set the initiator in the connector and let the volume drivers
return an error if iSCSI is required.

bug #1007084

Change-Id: I5da472e5013fdc0c733ecb12b919c1068873bdc6
(cherry picked from commit 3ba0c171c0b6f3516662bc0ab660b14cd6d34d8a)
Merge "Don't make nova-compute depend on iSCSI" into stable/grizzly