tests: Fix schema parser test for in-tree build

tests: Fix schema parser test for in-tree build

Commit 4f193e3 added the test, but screwed up in-tree builds
(SRCDIR=.): the tests's output overwrites the expected output, and is
thus compared to itself.

Cc: qemu-stable@nongnu.org
Reported-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(cherry picked from commit d8039e58b1ecfdc9af171502c83e3949f6dafb95)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>