Switch apache's reverse proxy config for gerrit back to ProxyPass

When trying to add users whose email addresses contained “+” to groups
in gerrit, apache changed the encoded “+” to a plain “+” in the PUT
Urls, which caused gerrit to not find the member in question, and
gerrit failed to add such users to groups.

We switch to the new suggested reverse proxy configuration provided by
Gerrit, which circumvents this problem.

Change-Id: Ifc88824cb1a83ba6ef4f0e9962f09f5d3368ea56
Merge "Switch apache's reverse proxy config for gerrit back to ProxyPass" into production