robustcheckout: retry on HTTP 5xx (Bug 1481291) r=sheehan

Differential Revision: https://phabricator.services.mozilla.com/D182008

--HG--
extra : moz-landing-system : lando

hgext/robustcheckout/__init__.py

@@ -498,6 +498,10 @@ def handlepullerror(e):
             ui.warn(b"ssl error: %s\n" % pycompat.bytestr(str(e)))
             handlenetworkfailure()
             return True
+        elif isinstance(e, urllibcompat.urlerr.httperror) and e.code >= 500:
+            ui.warn(b"http error: %s\n" % pycompat.bytestr(str(e.reason)))
+            handlenetworkfailure()
+            return True
         elif isinstance(e, urllibcompat.urlerr.urlerror):
             if isinstance(e.reason, socket.error):
                 ui.warn(b"socket error: %s\n" % pycompat.bytestr(str(e.reason)))