fix(tests): report curl output if it wasn't "Powered by Deis"

If the smoke test fails, it now reports what curl does see to the
test runner for help in debugging failures.

The smoke test now registers with the router rather than directly
to the controller at port 8000, and the .HostName config field was
more appropriately named to .Domain.

Fixes #1417.

TESTING: `export DEIS_EXAMPLE_APP=helloworld` (or another that doesn't end with "Powered by Deis") and run `make test-smoke`.
(separate concern from the bug, but thought I'd add that here)