Handle 404 and 409 response when deleting containers

Attempting to delete a stack with multiple SwiftSignalHandles will result
in a 409 error from Swift due to a logic error in the SwiftSignalHandle
resource. This change ensures that we properly handle 404 and 409
responses when deleting Swift containers.

Change-Id: Iac04bf16bce949dd5019975fd07e795cd0685eba
Closes-Bug: #1392867
Merge "Handle 404 and 409 response when deleting containers"