lib: don't close reader inside ReadStream
lib: don't close reader inside ReadStream

When aci.NewCompressedReader was changed to return a ReadCloser, we
changed the code in ReadStream to close it and then wrapped it with a
NopCloser. That was obviously wrong although it didn't seem to have any
effect.

Let's return the ReadCloser directly instead.

jsoriano/docker2aci,jonboulle/docker2aci,jsoriano/docker2aci,dgonyeo/docker2aci,vishvananda/docker2aci,dgonyeo/docker2aci,OMWAVE/docker2aci,appc/docker2aci,appc/docker2aci,OMWAVE/docker2aci,vishvananda/docker2aci,iaguis/docker2aci