Ibmvscsis Misc fixes

This change fixes reporting of correct OS back to client. It also
addresses getting a scsi scan to occur after SRP_LOGIN success.
I have also added a base_attrib as a target config op so that
it can be later used to check if tpg is setup prior to submitting
a login. A follow up task would be to get make_nexus to occur
during probe. This way target mapped luns and userspace stuff
is setup prior to handling of login request.