Serve cattrack using a cluster of mongrel instances

Currently we are serving cattrack using a single instance of mongrel. This serializes all access to the service which up until the current time has not been an issue as the server is not under a large load and none of the requests take too long to serve. As of r13810 the ability to query the output of test_case_executions was added and serving this request can take a long time. While that request is being served no other requests can be served which means the server can appear to hang.

We should serve the website with a cluster of mongrel instances so the website does not appear to be hung while running the queries. It should be a relatively easy configuration change (see [1] & [2]).

[1] http://mongrel.rubyforge.org/wiki/Apache
[2] http://mongrel.rubyforge.org/wiki/MongrelCluster