Additional exception type check for ceilo-client

This adds additional exception type checking for ceilometer client.
In addition to previous HTTPNotFound exception, ceilometer client lib
may throw an apiclient.NotFound exception directly.  Both cases should
be treated as 'valid' results from HTTP 404, so that the
ignore-not-found logic in Heat can work using either version of
ceilometer client.

Change-Id: Iedd061afe0cf039d5070257caf0d5a726213a8af
Closes-Bug: 1361128
Merge "Additional exception type check for ceilo-client"