If `wait=true` param is not set for delete vector API calls, a test asserting later
that data are gonna can become flaky, because at the assertion time the data could be
still there.
The following files contain such tests at the moment:
* `test_multi_vector_uint8.py`
* `test_multi_vector.py`
* `test_multi_vector_unnamed.py`
* `test_optional_vectors.py`
In order to fix these and prevent the flakiness of future test,
`request_with_validation` helper add `wait=true` param, if it is not set
for delete vector calls.