Setting Retry=0 on proxy pass

I believe the fix for [https://jira.ceh.ac.uk/browse/NBNV-1005](NBNV-1005) is to set retry=0. I suspect that the issue arose when apache flagged the tomcats to be in the error state. This could happen if a request comes in during a tomcat restart (web app deployment)

Unfortunately as stated on the issue, we can not at this time simply pass this parameter in using puppet code and therefore need to maintain a custom fragment which states the proxying setup.

If https://github.com/puppetlabs/puppetlabs-apache/pull/764 gets resolved, we can revert this change and use the new parameters.

But for the time being I think this is a sensible solution.