Trim trailing slash and version from endpoint

This commit removes trailing slashes and "/v1" from the endpoint
given when initializing the HTTP client, in order to fix the bug
mentioned below. It also removes the rstrip call in
_make_connection_url, since this is done up front now.

Also adds tests for get_connection_params.

Change-Id: If2c2cd766466dca4621e8daa260575fd4f106f06
Closes-Bug: #1342048
Merge "Trim trailing slash and version from endpoint"