stop killing antlir builds

Summary:
The actual chef run inside `antlir2` is run inside of a separate pid namespace,
so should be exempt from the killing spree
(https://github.com/facebook/chef-utils/blob/0a79708f837ed87a7c37e4419838ad6a2ee2b473/chefctl/src/chefctl.rb#L519),
but the top-level process has the substring `"chefctl"`, causing the outer
container process to be `SIGTERM`ed.

Differential Revision: D70514430

fbshipit-source-id: a0ebd9d828000a624a71e2e9cdea5d1383d4c3a2

Author: vmagro

chefctl/src/chefctl.rb

@@ -560,6 +560,8 @@ def chefctl_procs
             # Don't kill any ssh processes, but we might kill their children
             # separately. It'll get cleaned up if the child gets killed anyway.
             /ssh/,
+            # Don't kill antlir image builds
+            /antlir/,
             # Facebook-ism, ignore
             /sush/,
           ],