generator: Fixes for Android Boot environment

generator: Fixes for Android Boot environment

In Android Boot environment we do not parse ostree= karg to determine
what directory to boot into, alternatively we do this based on the
androidboot.slot_suffix= karg. But we do set ostree=true karg to denote
that we are indeed booting an ostree environment (required for some
systemd unit files). This change accounts for this approach in the
systemd generator. In this case androidboot.slot_suffix= points you to
/ostree/root.[a|b] and then that points you to the directory to boot
into in /ostree/deploy... Here is what a cmdline may look like in this
type of environment:

androidboot.slot_suffix=_a androidboot.bootdevice=*.ufshc root=PARTLABEL=system_a root=UUID=76a22bf4-f153-4541-b6c7-0332c0dfaeac rw ostree=true loglevel=4 acpi=off console=ttyAMA0 systemd.show_status=auto libahci.ignore_sss=1 slub_debug=FPZ fsck.mode=skip rcupdate.rcu_normal_after_boot=0 rcupdate.rcu_expedited=1

Signed-off-by: Eric Curtin <ecurtin@redhat.com>