Pass OEM property list to OTA tools, thumbprint.

The OTA generation scripts need to know what system properties to
read from the OEM partition, so pass along from product definition.

Also define "thumbprint" which is only the build-specific parts of
the fingerprint.  (Thumbs are smaller than fingers.)

Bug: 13367676
Change-Id: Iae051dcd2b1c67a7c8554d8ae318a4c54a86d614