puppetlabs-apache::mod::ssl - additional class parameters

Hi,

I would like to set some advanced Apache SSL directives using the apache::mod::ssl class:

• SSLSessionCache: this is already a template variable (`$session_cache`), but it's assigned within apache::mod::ssl and it's impossible to override. Solution would be to move the code block into apache::params and to add an apache class parameter to override defaults (exactly as the $apache::mod::passenger::passenger_root variable).
  Why ? On our web servers, we use a specific place outside of the var directory, something like 'shmcb:/tmp/ssl_session_cache(2000000)'

• SSLProxyProtocol is both a server and a virtual host directive, but currently it can be defined only on apache::vhost defined type, and I would like it to be present as a apache::mod::ssl class parameter. Default value would be undef which means no directive inside the generated ssl.conf file.
  Why ? We'd like to define this directive for all our vhosts instead of repeating it into each vhost.

I'm able to implement this as a PR on github if you're OK with my proposal.