Use ro.cm.display.version when reporting

People are getting confused because their CM version listed on their
CMAccount says "SNAPSHOT" when they are running an installer build.
They are asking why they are not running stable builds, however, the
installer snapshot builds are built off the stable branch.

Display version is more appropriate here.

Change-Id: Iad33e3ee5098c146fd77ccf06a708c4eec57b96d