Safer/more useful/++awesome phpunit tests
* Made a wrapper for potentially dangerous curl functions
(don't have to worry about somebody running unit tests on a dev
machine with 3rd party creds anymore)
* Overrode the curl_exec wrapper such that it will return
canned responses. This means we can now test response codes
and error handling without contacting anything.
* Added an example canned response in GC.
* Modified old GC tests such that they now pass with the new style
* changed extension on canned responses in the hope that Jenkins
will stop trying to lint them.

Change-Id: Ie2464118e9465bfbb3e2f803f3afdbb6a131a34a