include_credentials now appends --no-remove-secure

As pointed out by Andrew Hsu, the initial process of removing the secure directory resulted in an intermediate layer with the credentials still in it. This process will now strip out the credentials within the same layer.
Update CHANGELOG
cleanup docker_init specs
Merge branch 'tduffield/spec-cleanup' into tduffield/FSE-190

Conflicts:
	spec/unit/container_docker_init_spec.rb
Merge branch 'tduffield/FSE-188' of github.com:opscode/knife-container into tduffield/FSE-190

Conflicts:
	spec/unit/container_docker_init_spec.rb
Support private registry dockerfile names