Add client and server tests for empty (but not null) query string

[trask]

I think it's probably worth adding client and server tests for urls like http://host/path?, to make sure that client and server instrumentations capture the http.target correctly in these cases since typically http.target is reconstructed from query string, and it's an odd case of empty (but not null) query string.

[trask]

Closing, can revisit later if anyone has renewed interest.