Variable-based solr settings

gistfile1.php

<?php
/**
 * Implements hook_default_search_api_server_alter().
 *
 * Override the Solr server options to load from a variable.
 */
function example_default_search_api_server_alter(array &$defaults) {
  $defaults['drupal_solr']->options['host'] = variable_get('drupal_solr_host', 'localhost');
  $defaults['drupal_solr']->options['port'] = variable_get('drupal_solr_port', '8983');
  $defaults['drupal_solr']->options['path'] = variable_get('drupal_solr_path', '/solr/drupal');
}