Accept header treatment for transport files

[cristian-recoseanu]

Is it worth adding a test to check if nodes can accept or at the very least ignore and return a response for a client requesting the transport file and proving an Accept header of application/sdp?

We've seen cases where nodes return an error code when an Accept header of application/sdp is provided but return the response correctly if no Accept header is provided.

This probably requires both IS-04 manifest_href uri and IS-05 /transportfile uri's to be checked by the test suite.

[garethsb]

May also apply to other API endpoints in that they should accept Accept: application/json.