Have Quay lookup the sbin/my_init PID to kill

We changed the entry point in Quay to be a shell script that calls `my_init`, which means the init no longer has PID 1. We therefore need to look up the correct PID to kill it.

Fixes https://jira.coreos.com/browse/QS-74

endpoints/api/suconfig.py

@@ -3,6 +3,7 @@
 import logging
 import os
 import signal
+import subprocess
 
 from flask import abort
 
@@ -136,6 +137,21 @@ class SuperUserSetupDatabase(ApiResource):
     abort(403)
 
 
+# From: https://stackoverflow.com/a/44712205
+def get_process_id(name):
+    """Return process ids found by (partial) name or regex.
+
+    >>> get_process_id('kthreadd')
+    [2]
+    >>> get_process_id('watchdog')
+    [10, 11, 16, 21, 26, 31, 36, 41, 46, 51, 56, 61]  # ymmv
+    >>> get_process_id('non-existent process')
+    []
+    """
+    child = subprocess.Popen(['pgrep', name], stdout=subprocess.PIPE, shell=False)
+    response = child.communicate()[0]
+    return [int(pid) for pid in response.split()]
+
 
 @resource('/v1/superuser/shutdown')
 @internal_only
@@ -154,7 +170,7 @@ class SuperUserShutdown(ApiResource):
       if app.config.get('DEBUGGING') == True:
         return {}
 
-      os.kill(1, signal.SIGINT)
+      os.kill(get_process_id('my_init')[0], signal.SIGINT)
       return {}
 
     abort(403)