Allow system_server to kill crosvm/virtualizationmanager

VirtualizationManager (and indirectly crosvm) now runs as a child
process of the client, which could be a process forked from zygote.
As a result, these get tracked as phantom processes of the client and
system_server will try to kill them if it chooses to kill the client.

Currently this does not work because system_server is not allowed
sigkill for the corresponding domains. In theory, that should not be
a problem because virtualizationmanager will automatically kill any
crosvm instances and terminate itself if its parent dies, but we should
not rely on that fact and instead give system_server the ultimate
control over app process termination.

Bug: 269461627
Test: atest MicrodroidTestApp
Change-Id: Ie0ba5388d00a51812c9424c37f2f74983bea9db8
diff --git a/private/system_server.te b/private/system_server.te
index b3c7528..3cff939 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -102,10 +102,12 @@
 allow system_server zygote:fd use;
 allow system_server zygote:process sigchld;
 
-# May kill zygote on crashes.
+# May kill zygote (or its child processes) on crashes.
 allow system_server {
   app_zygote
   crash_dump
+  crosvm
+  virtualizationmanager
   webview_zygote
   zygote
 }:process { getpgid sigkill signull };