ability to pass extra parameters to the vhost

In some situation, it is useful to be able to pass extra parameters
to apache::vhost.
This change introduces a new parameter to pass a hash. It is use to
overwrite or add new parameters.

The variable uses an agnostic vhost_* name for the case we introduce
the support of a new server (e.g: nginx).

Closes-bug: #1294339

Change-Id: I749f005964c3bc549d724329d2dc9bc4f6dbcf6f
Merge "ability to pass extra parameters to the vhost"