iotests: fix 097 when run with qcow

iotests: fix 097 when run with qcow

The previous commit:

  commit a3e1505daec31ef56f0489f8c8fff1b8e4ca92bd
  Author: Eric Blake <eblake@redhat.com>
  Date:   Mon Dec 5 09:49:34 2016 -0600

    qcow2: Don't strand clusters near 2G intervals during commit

extended the 097 test case so that it did two passes, once
with an internal snapshot, once without.

qcow (v1) does not support internal snapshots, so this change
broke test 097 when run against qcow.

This splits 097 in two, creating a new 176 that tests the
internal snapshot codepath, effectively putting 097 back
to its content before the above commit.

Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <20170221115512.21918-8-berrange@redhat.com>
[eblake: test collisions: s/173/176/g]
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-id: 20170331185356.2479-2-eblake@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>