iotests: Remove a few tests from 'quick' group

A run of './check -qcow2 -g quick' on my machine produced only
two tests that took longer than 5 seconds; 178 took 18, and
189 took 7.  Remove them from the quick group.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
