Allow other manifests to define ::apache::mod{ 'ssl': }.

This will allow Apache from the httpd24 SCL on RHELish systems to
include the proper mod_ssl package while still letting ssl
::apache::vhost defines work as expected.

Add package_name param to ::apache::mod::ssl.

Add a test for the package_name parameter.

Update the package_name parameter test.
Allow overriding the detected $apache_name.

This will mainly be useful for supporting Red Hat Software Collections,
where 'httpd24-httpd' installs Apache 2.4 alongside Apache 2.2 in the
base repository. The $service_name parameter already allows
customization of the service to use, but not the package.

Document the ::apache::apache_name parameter.

Add a test for the apache_name param.
Merge pull request #819 from smerrill/feature/allow-different-apache-package

Allow overriding the detected $apache_name.
Merge pull request #818 from smerrill/feature/allow-mod-ssl-customization

Allow other manifests to define ::apache::mod{ 'ssl': }.