Exception handling is captured correctly when deleting a container.

When deleting a container that is not empty, the exception code
does not send the error message through exception.handle. Instead,
it raises an exception which causes an error when Horizon is no
longer in debug mode.

Change-Id: Iee8601c5b0f831b2dd598accfdc58cb8130cca13
Closes-bug: 1355405
Merge "Exception handling is captured correctly when deleting a container."