Change LOG.exception to LOG.info for skipped tests

The safe setup decorator was presenting skipException in the logs as an error
and so producing lot of noise in tempest.log.

Change-Id: Ia95d6b9dee4eaf4fc8de4bb128f958ef7f693844
Related-bug: #1344581
Merge "Change LOG.exception to LOG.info for skipped tests"
Merge branch 'master' of https://github.com/openstack/tempest