Add new wait-for-current-snapshots-create operation

[dliappis]

This commit adds a new runner WaitForCurrentSnapshotsCreate, with the
corresponding operation name wait-for-current-snapshots-create that
waits until all current snapshots for a given repository have completed.

Closes #1537

[pquentin]

Thanks! LGTM. Left two nits.

[pquentin]

Not sure the link to the pull request helps that much now that 8.3 is out? Maybe we can put in the TODO instead. So when the TODO gets removed, this gets removed too.

[dliappis]

The reasoning behind putting the PR link here is to clarify that this feature (optionally excluding the large number of indices from the response) is only available from ES 8.3.0 onwards.
The TODO, later on, is about the support in elasticsearch-py since currently the index_names parameter in the version that we use is not supported.

I have improved and moved the comment to the beginning of the conditional in e482d72 to make this clearer. The TODO remained as is.

[pquentin]

Here's a potential simplification:

Suggested change

	if int(response.get("total")) > 0:
	await asyncio.sleep(wait_period)
	continue
	break
	if int(response.get("total")) == 0:
	break
	await asyncio.sleep(wait_period)

Also this logic is untested, should we in tests first have a response with total > 0?

[dliappis]

Thanks added the simplification in 87b7040.

Also this logic is untested, should we in tests first have a response with total > 0?

Not sure I understood this comment, we do test with total > 0 e.g. in

rally/tests/driver/runner_test.py

Line 4029 in ac80c61

"total": 4,

and ensure we wait the right amount of times in

rally/tests/driver/runner_test.py

Line 4047 in ac80c61

assert es.snapshot.get.await_count == 2

[pquentin]

Thanks, sorry I missed this.

[michaelbaamonde]

I left a minor suggestion, but otherwise LGTM.

[original-brownbear]

LGTM!

[michaelbaamonde]

Latest commits also LGTM.

[pquentin]

Thanks! LGTM.

[dliappis]

Thanks everyone for the great feedback!