Now that F24 images are made with livemedia-creator instead of
livecd-creator, the kickstart parser has changed; the new kickstart
parser doesn't understand the $INSTALL_ROOT variable we'd been using in
%post --nochroot scripts. This commit fixes this by replacing
$INSTALL_ROOT usage with hardcoded /mnt/sysimage as docs suggest.
While at this, this commit also fixes a case where resolv.conf would be
incorrectly copied if it is a symlink, thanks to dgilmore for pointing
this out.
