[SCSI] libiscsi: handle init task failures.

Mgmt setup used to not fail so we did not have to check
the return value. Now with cxgb3i it can so this has us
pass up a error.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>