Newer pip sets cache-control: max-age=0 on requests for pypi indexes.
This tells the proxy cache not to serve the index content from the
cache. Unfortauntely this then means we fail to get this data which
could be cached if we can't talk to the backend for some reason.
By default pypi seems to set a 600 second max-age on these indexes which
should be far better than not caching at all. So set the config to have
apache ignore client side max-age and other cache disabling directives.
Change-Id: I2da7006dcd8a8f4212f5e766ef35ba7b98177ed0
130c0a47fc