tools/init-xenstore-domain: support xenstore pvh stubdom

tools/init-xenstore-domain: support xenstore pvh stubdom

Instead of creating the xenstore-stubdom domain first and parsing the
kernel later do it the other way round. This enables to probe for the
domain type supported by the xenstore-stubdom and to support both, pv
and pvh type stubdoms.

Try to parse the stubdom image first for PV support, if this fails use
HVM. Then create the domain with the appropriate type selected.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>