Add install-multiple to adb.

The new install-multiple command automates creating an install
session, streaming multiple files into place, and then committing
or destroying the session.  This uses the recent "exec" feature to
stream APK contents over stdin directly into their final resting
place, requiring no extra copies.

Blindly pass through command line arguments to "pm" to make adding
new flags easier in future.

Remove support for verifying APK before sending across wire, since it
was reading the entire APK into memory (!) before sending.  Also
remove encrypted APKs, since they are no longer supported.  Drop
support for undocumented verification files.

Bug: 14975160
Change-Id: I0c538471873061798160e2e47cec4c0424c27361