Test failures caused by setting UTC in timezone

[LeeDr]

We occasionally see test failures (usually in Visualization tests) where the test suite (from the before method) logs;

Error: expected 'Browser' to equal 'UTC'

This is a check which was put in place to see if we were having problems with the timezone. The problem is that we unload (delete) the kibana index before almost every test suite and recreate an empty one, and we include a config doc with 'dateFormat:tz': 'UTC'

The problem is that Kibana might try to access it's index, see that it's missing, and go to create it, while the test is also creating it. So somehow we end up without our timezone set.

I don't have a good measure of how often this causes a test failure. Maybe there's a way to search?

1. One possible solution is to set the timezone the old fashioned way through the UI. But this slows down tests and we were already trying to go the other way and have the tests load visualizations by writing directly to the Kibana index.
2. Another possible solution is to make this check for the timezone also fix it if it's not set. Feels like a hack.
3. We could try to update the 'natural' Kibana config doc instead of creating it.

[LeeDr]

@rashidkpc FYI. I'll file others as they come up.

[LeeDr]

#7369 Switch Discover and Settings tests to use esClient to wipe .kibana review test

Addressed by these 3 PRs. There are still a couple of API tests which reload the .kibana index that still need to be changed.

#7346 Use elasticdump to preload default index for visualization tests.

#7298 New dashboard tests using elasticdump review test