Don't replace "!" with "/" for cciss until after size calculation

We use /sys/class/block/${tgtdrive}/size to calculate target drive size.
Unlike device files in /dev, paths in /sys have "!" instead of "/", so
the substitution should not be made until we're done with /sys.

Change-Id: If88c311ceb41e6e3e00ef7e536329477d4243ea7
Closes-bug: #1312311