Avoid restarting a child when terminating

When sending a SIGTERM to the main glance-api process,
it was sending a SIGTERM to its children
but then also re-spawning its first dead child.

Closes-bug: #1714240

Change-Id: Ibef426c198d287bbdac4e764fd654edba4b7c2d6
(cherry picked from commit 877cd166b5)

glance/common/wsgi.py

@@ -491,6 +491,7 @@ class Server(object):
         """Kills the entire process group."""
         signal.signal(signal.SIGTERM, signal.SIG_IGN)
         signal.signal(signal.SIGINT, signal.SIG_IGN)
+        signal.signal(signal.SIGCHLD, signal.SIG_IGN)
         self.running = False
         os.killpg(self.pgid, signal.SIGTERM)