sync: add a 5 second timeout to gemato's openpgp refresh

If it takes more than 5 seconds to download a miniscule file from
https://gentoo.org/.well-known/openpgpkey/ then something has gone
dreadfully wrong. Most commonly, what went wrong is that the user has
broken ipv6 connectivity and requests simply hangs forever (no joke --
it doesn't implement Happy Eyeballs and closed the multiple bug reports
as "please use stackoverflow to ask questions about how to use requests,
we are not a support forum").

Pass a timeout so that we eventually give up and try ipv4 instead. This
is a crude hack and the proper solution is to make gemato handle this
better, but until gemato is fixed to use a better download library we do
the best we can.

Bug: psf/requests#6788
Bug: projg2/gemato#35
Bug: https://bugs.gentoo.org/779766

lib/portage/sync/syncbase.py

@@ -340,11 +340,11 @@ def _get_openpgp_env(self, openpgp_key_path=None, debug=False):
 
             if openpgp_key_path:
                 openpgp_env = gemato.openpgp.OpenPGPEnvironment(
-                    proxy=proxy, debug=debug
+                    proxy=proxy, debug=debug, timeout=5
                 )
             else:
                 openpgp_env = gemato.openpgp.OpenPGPSystemEnvironment(
-                    proxy=proxy, debug=debug
+                    proxy=proxy, debug=debug, timeout=5
                 )
 
             return openpgp_env