Update Gerrit proxy configuration.

Replace the apache reverse proxy configs with the recommended
settings from the gerrit documentation[1].

Explicit use of ProxyPassMatch <URL> ! is used to handle cases
where we do not want to proxy through to gerrit (such as for
'^/p/') where an offload is expected/desired.

Using RewriteRule was causing the double slashes in Gerrit url
(i.e. https://review-dev.openstack.org//#/q/status:open).
Removing it fixes this issue. Similarly, the gerrit.token query
parameter was being dropped when the RewriteRule was used. More
explanation can be found in gerrit upstream bug[2].

[1] https://gerrit-review.googlesource.com/Documentation/
    config-reverseproxy.html#_apache_2_configuration
[2] https://code.google.com/p/gerrit/issues/detail?id=3365

Change-Id: Ied8ce7a0389253c10225a8bf3671f09a879bb061
Co-Authored-By: Khai Do <zaro0508@gmail.com>

templates/gerrit.vhost.erb

@@ -16,7 +16,7 @@
 <VirtualHost *:443>
   ServerName <%= scope.lookupvar("gerrit::vhost_name") %>
   ServerAdmin <%= scope.lookupvar("gerrit::serveradmin") %>
-  AllowEncodedSlashes NoDecode
+  AllowEncodedSlashes On
 
   ErrorLog ${APACHE_LOG_DIR}/gerrit-ssl-error.log
 
@@ -51,17 +51,21 @@
   RewriteCond %{HTTP_HOST} !<%= scope.lookupvar("gerrit::vhost_name") %>
   RewriteRule ^.*$ <%= scope.lookupvar("gerrit::canonicalweburl") %>
 <% end -%>
+
+  ProxyRequests off
+  ProxyVia off
+  ProxyPreserveHost on
+
 <% if scope.lookupvar("gerrit::replicate_local") -%>
-  RewriteCond %{REQUEST_URI} !^/p/
+  ProxyPassMatch ^/p/ !
 <% end -%>
 <% if scope.lookupvar("gerrit::contactstore") == true -%>
-  RewriteCond %{REQUEST_URI} !^/fakestore$
+  ProxyPassMatch ^/fakestore$ !
 <% end -%>
 <% if scope.lookupvar("gerrit::robots_txt_source") != "" -%>
-  RewriteCond %{REQUEST_URI} !^/robots.txt$
+  ProxyPassMatch ^/robots.txt$ !
 <% end -%>
-  RewriteRule ^/(.*)$ http://localhost:8081/$1 [NE,P]
-
+  ProxyPass / http://localhost:8081/ nocanon
   ProxyPassReverse / http://localhost:8081/
 
 <% if scope.lookupvar("gerrit::robots_txt_source") != "" -%>