Also keep around /var/home by default

A lot of backstory here, but essentially, we want Ignition to be able to
add users in RHCOS. This requires `/var/home` existing. To do this,
we either need to run systemd-tmpfiles, like FCOS, or just leave it
hanging around after Anaconda.

Since we're already doing the latter for `/var/lib` and `/var/log`, this
patch just extends it for `/var/home`. It's just easier to do this for
now rather than more involved fixes. This will be fixed the proper way
once RHCOS is bumped to spec 3 and inherits all the work that happened
in FCOS to support it.

Some more information about this in:
coreos/ignition-dracut#79

src/gf-anaconda-cleanup

@@ -50,10 +50,14 @@ done
 # see https://github.com/coreos/ignition-dracut/pull/79#issuecomment-488446949
 # For now we retain just /var/lib/systemd (for the random seed) and /var/log
 # for the journal, which init before systemd-tmpfiles.
+# Also just leave /var/home and /var/roothome; this allows early Ignition in
+# RHCOS to add users and drop files in /root.  (On FCOS, we don't strictly
+# *need* this because we run systemd-tmpfiles).
 var="${stateroot}/var"
 coreos_gf ls "${var}" | while read -r x; do
   case "$x" in 
     log|lib) continue;;
+    home|roothome) coreos_gf glob rm-rf "${var}/${x}/*";;
     *) coreos_gf rm-rf "${var}/${x}"
   esac
 done