Before this change serving bucket based objects
`[remote:bucket]/path/to/object` would fail with 404 not found.
This was because the leading `/` in `/path/to/object` was being passed
to NewObject.
Tests have been randomly failing with messages like
listen tcp 127.0.0.1:51778: bind: address already in use
Rework all the test servers so they choose a random free port on
startup and use that for the tests to avoid.
