su: Setting root access to "ADB only" doesn't work

Issue: http://code.google.com/p/cyanogenmod/issues/detail?id=5897

1. Settings > Developer Options > Root access > ADB only
2. Reboot device, just to be sure.
3. Plug the phone via USB to a computer capable of running adb.
4. Run adb shell. Results follows.

This change does:

- Add constants for CM Su Settings
- For app access, check that uid is not shell or root (this is when shell gains access
and then do a su from root)
- Hide shell and root UI deny/allow messages. This are always from background task (adb or
su from root) and messages are always on logcat. Only apps messages are shown.

Change-Id: Ib3cce944adb8810f49997add8beb628ea978af93
Merge remote-tracking branch 'refs/remotes/cm/mr1.1-staging' into jb-4.2

Signed-off-by: travp624 <travp624@gmail.com>