Bugfix swift delete vault

- Expands the implementation of the mock swift client's delete_container to more accurately reflect the documentation from swift
- Adds testing of the swiftclient throwing ClientException in the various calls we make to it
-- enabled via a control variable in the mock swift client that causes all mocked called to only throw the exception
-- adds a new test that only checks for the exceptions to be thrown by the mock client, and is specific to the mock client. Test is disabled if using the actual swiftclient
- Added an explicit test for deleting a non-existent block; required only to exercise the branch paths for coverage