wire up HTTP so we can test the mock discovery service
test lookupModuleVersions
Add a versions endpoint to the mock registry, and use that to verify the
lookupModuleVersions behavior.
lookupModuleVersions takes a Disco as the argument so a custom Transport
can be injected, and uses that transport for its own client if it set.
test looking up modules with default registry
Add registry.terrform.io to the hostname that the mock registry resolves
to localhost.
ACC test looking up module versions
Lookup a basic module for the available version in the default registry.