Catch ClientErrorException may do nothing when request is POST mode. #55

In class AbstrDockerCmd. Method exec() want catch ClientErrorException to handle http status other than 200(Some error happend). But this may only work when do GET method.
For example, DockerClient.inspectContainerCmd(containerId) method use HTTP_GET method and work well. But if we call DockerClient.stopContainerCmd(containerId) method and try catch NotFoundException or/and NotModifiedException to get stop operation result. This issues will cause we always got nothing even though target container not exist.

Sorry for my poor English...