Update caching proxy squid configuration

broken_vary_encoding is no longer recognised as a configuration
directive.
0.0.0.0/0.0.0.0 has internally been converted to all so that line is not
needed
CIDR notation prefered to netmask (squashes warning)
spool dir changed

Change-Id: I866ec5c0e76a5fb242aaf2becafa69357e52bb12