Fixing flaky alert deletion tests (elastic#226281)

Fixes elastic#226076
Fixes elastic#226074
Fixes elastic#225725
Fixes elastic#225280
Fixes elastic#224985
Fixes elastic#224934
Fixes elastic#224742
Fixes elastic#224675
Fixes elastic#224670

Fixes elastic#224135
Fixes elastic#223437
Fixes elastic#223364

## Summary

The first 9 issues were flaky with error `Error: expected 200 to sort of
equal 204`. This is caused by this PR
elastic#223336 which has the schedule API
return a 200 if an instance of the task was already running for the
space. This flakiness should be fixed by retrying the schedule request
until a 204 is achieved.

The last 3 issues were flaky before the prior PR was merged so I suspect
they ran into the same issue (where another instance of the task was
already running so the new task was not kicked off but no indication of
this was returned).

Author: ymao1