Skip negative tests of v3 server metadata

If sending long metadata to "create a server" API of Nova v3 API,
the API returns an OverLimit response now.

However the commit Ic17d2227909c9180ca86c9d578dad4c73ec57dfc will
change the response to BadRequest. To verify the commit on Jenkins,
it is necessary to skip the tests related to long metadata temporary.

Change-Id: Ic03c2247505780fbeda68e908298a98862ea0c7c
Related-Bug: #1273948
Merge "Skip negative tests of v3 server metadata"