build: Add support for vendor product and device name

 * CM's build system assumes some convention-over-configuration which
   we might need to override in order to conform to vendor requirements.
 * Allow overriding of target and product names using these new
   variables. This allows for CM conventions to work, while generating
   the correct fingerprint dynamically without post processing the
   strings.

Change-Id: Ic5913e587400dd38c04aa05de3a7becced77a59e
merge changes from CyanogenMod 10.2 into local branch