Add script and module to run tempest with xunit and skip file

The skip file, if supplied, allows specification of regexs to include or
skip.

Change-Id: Ie2f02b257fb5aba5ea1e16d944c3b86ca66d3236
(cherry picked from commit 7b41b5c1c595533446d5073e5693a0e76ba8e3ea)