sepolicy: Allow Sensors daemon to access sensors folder and start diag_mdlog

The Sensors daemon will create an incoming named pipe which will cause it to
flush the DIAG buffer.  This named pipe will be co-located with other
Sensors files, used by other Sensors processes.

The Daemon will also invoke diag_mdlog, in order to support on-device message
logging by default.

Change-Id: I10245155fd8387a9cf460842682be360dd70707f