Allow to signal perfetto from shell.

When daemonizing perfetto, SIGINT should be sent to ensure clean
shutdown.

Denial:
12-06 11:12:16.566  3099  3099 I sh      : type=1400 audit(0.0:462): avc: denied { signal } for scontext=u:r:shell:s0 tcontext=u:r:perfetto:s0 tclass=process permissive=1

Test: m
Test: flash walleye
Test: SIGINT perfetto from shell

Change-Id: I8d34b447ea90c315faf88f020f1dfc49e4abbcce