Use a variable to store the search_api_solr service class which defaults to the Pantheon service class.
Clean up variables to remove legacy search_api_solr variables.
Override search_api server configuration form to make it clear that Pantheon is managing the Solr connection settings, and that the regular search_api server settings are not used
Merging changes from scor to use a pantheon_apachesolr_search_api_solr_service_class variable.
Override search_api server configuration form to make it clear that Pantheon is managing the Solr connection settings, and that the regular search_api server settings are not used

Another pull request from scor! :)