Also, refactor ietadm/tgtadm calls out into helper classes. Add a new
TargetAdmin abstract base class and implement it using ietadm and
tgtadm. This cleans up the code greatly and gets us some code reuse.
(Based on a patch by Chuck Short <zulcss@ubuntu.com>)
Change-Id: I1c0064e5d35483a6c4059cfc61a484f5f576b2da