Host can continue to update lease after losing partition.

[serkantkaraca]

Actual Behavior

1. Host A steals the lease from host B.
2. Host B keeps updating the Azure blob lease with bogus check-pointing data.

Expected Behavior

1. Host B should not be able to update the lease if it already lost the partition ownership.

Issue is due to downloading Azure blob lease before each checkpointing. This way host continues to access newly generated token and updates lease with bogus checkpoint.

[serkantkaraca]

Fix merged into dev branch