tests: change /0.15/* tests to /qmp/*

tests: change /0.15/* tests to /qmp/*

Presumably 0.15 was the version it was first introduced, but
qmp keeps evolving. There is no point in having that version
as test prefix, 'qmp' makes more sense here.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180326150916.9602-12-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>