BannedFilesTest: Add "init_runit"

Adds a test for the init_runit engineering backdoor
that allows attackers to execute shell commands as
root. Found in some Sharp and Motorola devices.

CVD-2013-4777
https://plus.google.com/110348415484169880343/posts/5ofgPNrSu3J



Change-Id: Ibd71ec4d0564ca272a6d21f12eb6dd7540a14675
Signed-off-by: Jon Sawyer <jon@cunninglogic.com>