Cancel outstanding requests when new time period is selected

[chrisronline]

This is mainly for discovery.

Scenario:

1. Change the time period in the time picker
2. Wait for data to fetch
3. While waiting, change the time period
4. Expect the results to match the most recently updated time period, but instead, it matches the first one

We need to cancel outstanding requests when the time period is changed.

[stacey-gammon]

I think I just ran across a similar issue. While the data was loading I turned on a filter. Then the data didn't match the filter:

I actually have been noticing a ton of weird behavior on this page, including losing all my columns and my search sporadically. Can't seem to repro that. And am hitting #9571 as well which may be interferring.

cc @elastic/kibana-discovery

[Bargs]

I agree the UI and the data should never be out of sync.