* Update drill+sadrill to specify an SA URL parm of "impersonation_target".
Sqlalchemy-drill is being updated to support impersonation with the
drill+sadrill driver, where previously it did not. The way that callers
should specify impersonation matches that for the drill+jdbc driver in that
a SA URL parameter of impersonation_target should be set to the username
of the user to be impersonated, while the stadard SA username and password
should be those of the proxy user.
* Remove lint.
* Address review comments.
* Use idiomatic pytest to test for a raised exception.
* Fix import statement order in drill.py.
