Convert headers to bytes testing request_headers

In requests 1.2 and python 3 headers are bytes so we need to optionally
convert unicode text to bytes when testing that the request headers
match those being checked for.

Change-Id: I02dadc05dd5a93769da646686b938c2b26f6f267
Closes-Bug: #1361528
Merge "Convert headers to bytes testing request_headers"