Add move to object client + change datasets.mv

[jkeelan]

This PR adds move to the object client, using the object-move endpoint.

This reduces the number of API calls for datasets.mv. I've tested the functionality and it seems to work as expected.

[imrehg]

Can this and #162 combined maybe? Or either way have to keep that other one in mind for this change too, right?

[jkeelan]

Yeah. Either combine or I'll merge once #162 hits master.

[acroz]

LGTM, left a few comments.

An important thing to note is that this move endpoint works asynchronously - the lifetime of the request looks like:

• Receive request
• List all files under the source path
• Work out all the above files' destination paths and dispatch individual move operations to a queue
• Request completes
• The service churns through the queue of operations to complete

At the very least, the fact that this operation is asynchronous should be well documented. We should also consider whether it is acceptable to change the behaviour of datasets.mv - users of this interface may rely on it blocking until complete in scripts etc.

[acroz]

Nit: remove extra blank line

[acroz]

This should re-raise the original exception if the error code does not match:

Suggested change

	if err.error_code == "source_path_not_found":
	raise PathNotFound(source)
	if err.error_code == "source_path_not_found":
	raise PathNotFound(source)
	else:
	raise

[acroz]

Since this also functions as the main test of ObjectClient.move, I suggest naming this:

Suggested change

	def test_object_client_move_url_encoding(mocker):
	def test_object_client_move(mocker):