snapuserd: Handle real time signal 36

Add a signal handler for real time signal 36 which
is primarily used by profilers. Default action is to
terminate the daemon if there is no signal handler. We
don't want daemon to get terminated, hence just capture
the signal and ignore it.

Bug: 201497662
Test: cow_snapuserd_test, pkill -36 snapuserd
Signed-off-by: Akilesh Kailash <akailash@google.com>
Change-Id: Ife5a8bdb7344956076bc4223c19a126b90a00706