Duplicated lease name should return HTTP 409 Conflict instead of HTTP 500

[Michał Kamiński]

Currently when user tries to create a lease with duplicated name,

Error
HTTP/1.1 500 INTERNAL SERVER ERROR {"error_name": 500, "error_message": "ClimateDBDuplicateEntry: A database error occurred", "error_code": 500} is presented, but should return

HTTP 409 CONFLICT
 {"error_name": "Duplicated Lease Name", "error_message": "Lease with name %lease_name already exists", "error_code": 409}

[Michał Kamiński (michal-kaminski)]

Fix proposed to branch: master
Review: https://review.openstack.org/#/c/85678/

[Michał Kamiński (michal-kaminski)]

(09:44:55) openstackgerrit: A change was merged to stackforge/climate: Duplicated lease name should return HTTP 409 https://review.openstack.org/85678