Fixup regressions in PureISCSIDriver log statements.

There were some conflicting patches that went in to fix i18n helpers,
and in the merge resolution we lost some changes that previously removed
all uses of .format() from the driver. This puts back in the updated
log statements originally added in 
https://review.openstack.org/#/c/135047/

Change-Id: I562a0dd950b88af2bdb67a135f6f6f0d258eed0e
Closes-Bug: 1395060
Merge "Fixup regressions in PureISCSIDriver log statements."