Test #ldpr-get-options using the OPTIONS HTTP method (not GET)

The test testGetResponseHeaders references the spec testing for HTTP OPTIONS headers, but tests it using HTTP GET.

This pull-request changes the request method to OPTIONS to align with the spec.

4.2.2.2 LDP servers MUST support the HTTP response headers defined in section 4.2.8 HTTP OPTIONS. 
http://www.w3.org/TR/ldp/#ldpr-get-options