(bug 55127) Implement network timeouts

A hung connection will now raise an SSLError (or equivalent
for HTTP connections) after 120 seconds (config.socket_timeout)

Change-Id: Ief38beaf912d4dd1c267eff46e2b73bff8edc447
(bug 55127) Allow user to cut off pending network requests at shutdown

If an exception was raised, an extra message is shown to the user,
suggesting to use ctrl-c to abort processing. Otherwise this message
is only shown if the bot is running in verbose mode.

Change-Id: Ie5cf53f97877e61c30e19e10cc2c0fdee647dcac
(bug 55127) Allow user to abort during http request

KeyboardInterrupts are only processed during Python code, and
thus not during lock acquisition.

Change-Id: Ieea4a9d35ae7b26921584f4b52e4c2f7cf2e63d0