Review consistency of ADLS python client used for Impala testing

The ADLS Python client seems to have consistency issues even though ADLS claims to be strongly consistent.

Some of our tests are skipped because of this issue, with the tag SkipIfADLS.slow_client.

The documentation for the Python client doesn't seem to state or address this as a known issue. It is however, a pre-release client.

This JIRA is meant to track this issue on the Impala side, and close it once it's addressed by ADLS.