Allows init to send signals.

This will allow init to terminate services cleanly (SIGTERM, wait,
SIGKILL) when needed.

Bug: 26216447
Test: manual: init is able to send a SIGTERM signal without denials.

Change-Id: Id2471ca08c0b011be64a36956628e965bc999bc6
diff --git a/init.te b/init.te
index 24fdee8..7346d9a 100644
--- a/init.te
+++ b/init.te
@@ -177,7 +177,7 @@
 
 # Support "adb shell stop"
 allow init self:capability kill;
-allow init domain:process sigkill;
+allow init domain:process { sigkill signal };
 
 # Init creates keystore's directory on boot, and walks through
 # the directory as part of a recursive restorecon.