Allow a manually set remote address for a fake request

Provides a quick way to change the remote address for a fake request. I needed to simulate different IP-addresses for security-tests.
@gmethvin I thought about that for consistency, but unlike a header or body which are added to the fake request ("with"), the remote address is just changed and a request is coming "from" an address. I therefore chose to break with the consistency on purpose because it was sounded more natural to me, however, if you prefer "with" I don't really have a problem with it, let me know and I change it!