Updater: Show update's version on AlertDialog and Notification

Currently at most of the places, build version is obtained from BuildInfoUtils.getBuildVersion()
method. This method obtains build version from the current running system's property.

However, in case there is a version bump on OTA, this logic results in wrong version
being shown to the user while updating/upgrading the system.

Get the version from the update itself to show the proper version in update notification
and pre-install warning.

Signed-off-by: Aayush Gupta <theimpulson@e.email>
Change-Id: Ia74085d8d7c067c408e7cfce1de90d49dcc68307