Schematize ADB system properties

Properties accessed across partitions are now schematized and will
become APIs to make explicit interfaces among partitions.

Bug: 117924132
Test: m -j
Change-Id: Iec37f5f35b1452afdf7b15e9f31c4b4726127065
Merged-In: Iec37f5f35b1452afdf7b15e9f31c4b4726127065