Don't assume All LDP Servers will respond with turtle

The test suite should set an Accept header of text/turtle whenever it wants Turtle format and should not assume all LDP servers will implement 4.3.2.2 [SHOULD].

4.3.2.2 LDP servers SHOULD respond with a text/turtle representation of the requested LDP-RS whenever the Accept request header is absent.
http://www.w3.org/TR/ldp/#h5_ldprs-get-conneg