Properly handle git-http-backend in zuul class
Properly handle git-http-backend in zuul class

In order to avoid the following issues:
- "Cannot get script name, are DOCUMENT_ROOT and SCRIPT_NAME (or
  SCRIPT_FILENAME) set and is the script executable?"
- "fatal: GIT_PROJECT_ROOT is set but PATH_INFO is not"

when running zuul merger under Nginx, its required to change
/add specific fastcgi_params in that vhost. Thus, adding:
- DOCUMENT_ROOT
- GIT_PROJECT_ROOT
- PATH_INFO
fcgi parameters.

Change-Id: Ia974668db96368965db849830e3f689455a84168

fuel-infra/puppet-manifests,fuel-infra/puppet-manifests,fuel-infra/puppet-manifests,fuel-infra/puppet-manifests