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



(cherry picked from commit b5ea5285)

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

Conflicts:
	tests/plans/CTS-flaky.xml

Change-Id: I7063c139762e03b1dfd6b0d6ae17070815132b31