Extend pm to support sessions and split APKs.

Separate commands to create an install session, stream files into the
staging area, and then commit the install.  Streaming can accept data
from stdin across adb, avoiding extra copy from push.

Extend FileBridge to support blocking close().  Always destroy
session regardless of result.

Bug: 14975160
Change-Id: Ic3f462e7d1901079b785e210228950cdfa676466