device-introspect-test: New, covering device introspection

The test doesn't check that the output makes any sense, only that QEMU
survives.  Useful since we've had an astounding number of crash bugs
around there.

In fact, we have a bunch of them right now: a few devices crash or
hang, and some leave dangling pointers behind.  The test skips testing
the broken parts.  The next commits will fix them up, and drop the
skipping.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1443689999-12182-8-git-send-email-armbru@redhat.com>