Updating datastore HTTP wrapper.

[dhermes]

• Making the method arguments (both in position and name) match the arguments for google.cloud.datastore_v1.gapic.datastore_client.DatastoreClient
• Passing positional as positional and keyword as keyword when using the low-level API client in Client.get() (was previously using all keyword arguments to .lookup(), which caused this issue)
• Updating mock call assertions to match the change in calling behavior.

Fixes #4387.

[dhermes]

When I checked the datastore_client.DatastoreClient interface, this also revealed

• Our low-level HTTP client doesn't have retry= or timeout= keywords (@jonparrott any good ideas here?)
• Our low-level HTTP client doesn't support the reserve_ids method

[tseaver]

Ugh, it feeds a little B&D / un-Pythonic to insist on "positional-only" args. Having the underlying bits change their argument names is actually a bit of a foul. I guess this is "not user-facing", so we can go ahead.

[dhermes]

@tseaver I think it's "good form" to do. With the addition of keyword-only arguments in Python 3, I'm not so sure that's a common attitude. From my perspective, using positional as positional and keyword as keyword actually indicates that the knows that.

Also, this isn't the first time we've been bitten by the auto-generated interface changing, which is why I advocate for "strict" adherence the offered interface.

PS What's B&D?

[tseaver]

@dhermes note that I approved the PR: I'm just "arguing with the ref."

Also, this isn't the first time we've been bitten by the auto-generated interface changing, which is why I advocate for "strict" adherence the offered interface.

They are equally capable of breaking this usage (changing order of "positional" arguments, for instance, which would be covered by using only keyword args when calling them).

B&D -> "bondage-and-discipline".