(This is a merge of http://go/wvgerrit/11613 from the Widevine CDM
repo.)
Adds a property for the OS version, implements it on Android, and
adds it to the license request property bag so that Netflix may
use it to discern the supported capabilities of the CDM.
Bug: 18230738
Change-Id: If5174a108093855314f3e0102b83691e20bb247b