Fix Availability Group Name validation in MS SQL Cluster form.

Fixes: bug MRN-881
Cherry-picked from 098d84a4da842dea24714589fe4f8a763ccb4c45
(gerrit link I5ced0dc76ad57dda9826b355064cc00718c93179)

Change-Id: I510c224a0d09e5d97199155532be659d080a5c13