Add test to properly catch debian/sid strings from version

strings for wheezy/sid and jessie/sid aren't caught by the version number
 test already implmented.

Adds test to check if codename is still empty and version contains a slash
 if so, and minor is sid, we set codename to sid. Otherwise we set codename
 to major.

Futher assessment may then made to see if we should then refuse
 jessie or sid

Signed-off-by: Andrew Woodward <awoodward@mirantis.com>