Catching no handled exception on leases deletion

Catching Conflict exception coming from NovaClient when creating
an image is not possible due to invalid vm_state.
Also, adding new test to cover the scenario being fixed.

Closes-Bug: #1299467
Change-Id: I22113ebebed74e72578fbc6baecdd8d0a462bf22
Merge "Catching no handled exception on leases deletion"