Add a protocol test for endpoints that contain path prefixes

[adamthom-amzn]

Description of changes:
Sometimes, a service will have a path prefix that is not modeled. This adds a
test that ensures REST-JSON clients will properly take that path into account.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[gosar]

PathOperation reads like an operation with path parameters. Maybe EndpointWithPathOperation? Or if that implies use of @endpoint trait like the couple of tests above, maybe HostWithPathOperation?

[mtdowling]

Suggested change

	uri: "/custom/PathOperation",
	uri: "/custom/HostWithPathOperation",

[adamthom-amzn]

Yeah, that was a bad miss.

[mtdowling]

Can you flip this sentence around and say when it would a path, an example of what it looks like, and how it works with paths in operations? It's important to state that here since we aren't using the same URI resolution logic defined in RFC 3986.

For example:

host MAY contain a path to indicate a base path from which each operation in the service is appended to. For example, given a host of example.com/foo/bar and an operation path of /MyOperation, the resolved host of the operation is example.com and the resolved path is /foo/bar/MyOperation.