Add methods to get and ensure encryption policy.

Add methods to get and ensure encryption policy.

The ensure call will either assign an encryption policy, or verify
that an existing policy matches the expected value.  Uses the new
logging library so that customers can pivot logs into whatever
location they want: vold into logcat and init into dmesg.

Also add new directories that will have user-specific encryption
policy set on them so we avoid setting the default policy.

Bug: 25796509
Change-Id: Ia535630092822c80cde0939d8e46e6b47d9be2d8