Webtests fail on external site

The original intention of our webtests were that they would simply drive a web-browser and test the functionality of a CiviCRM site (on any server).

Somewhere along the line our webtests have become encumbered with dependencies on a local server which cause them to fail in any other context. Those dependencies are:

• CiviSeleniumTestCase::__construct() bootstraps CiviCRM locally
• CiviSeleniumTestCase::webtest_civicrm_api() makes civicrm api calls to the local server
• About a half-dozen tests rely on internal functions like CRM_Core_DAO::singleValueQuery()

Proposed solution:
1) Change the webtest_civicrm_api() function to use the REST api of the remote server instead of the local api
2) Remove all calls to internal CRM_ functions and use the api instead
3) Don't bootstrap civicrm in webtest environment