mel.conf: update SANITY_TESTED_DISTROS

Currently, we do not support CentOS 6 due to its lack of the needed python
2.7. We also do not support Debian, SUSE, or openSUSE at this time.

JIRA: SB-1262

Signed-off-by: Christopher Larson <kergoth@gmail.com>
Merge pull request #50 from kergoth/update_sanity_tested_distros

mel.conf: update SANITY_TESTED_DISTROS