Install splash.xpm in the right location on iSCSI installs

Previously, we copied splash.xpm to /liveos in all cases. Put it
on the proper boot volume if it's an iSCSI install.

Change-Id: I7e027c290e9c69e1395739597097ce289f3787ac
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=924527
Signed-off-by: Ryan Barry <rbarry@redhat.com>