Tests with inputs, descriptors available via HTTP

[david4096]

The workflow service can download workflow descriptions that provided as HTTP links. To properly test this surface we should host a workflow description via a SimpleHTTPServer or similar.

This could also be used to test workflows that have inputs that must be downloaded/provisioned, by hosting the inputs needed to perform the test.

To close this add integration tests that show the different ways workflow descriptors can be provided (both HTTP and string).