Changing PureISCSIDriver to use % string formatting instead of .format

Removing usage of .format for string formatting to be more in line with
OpenStack standards. Adding appropiate usage of _LE,_LW,_LI as well.

Change-Id: I4f411920293553d1356012c7db803c9b2dcf593f
Closes-bug: #1392063
Merge "Changing PureISCSIDriver to use % string formatting instead of .format"