add timeouts to galaxy urllib2 calls

(minor patch)
I had a situation where a firewall was blocking any outbound connections.
ansible-galaxy was hanging indefinitely with zero output. Some debugging
showed where it was hanging.

I initially put this in as an opt, but since there isn't a class being
passed around it's much simpler to just use a const.

Tested by setting the timeout very short to make sure it works as expected.