Fixed malformatted request when using empty list in create_container()

create_container() sends a malformatted request when volumes==[] or
ports==[], causing error 500 "create: ExportEnv json: cannot unmarshal
array into Go value of type map"

The empty lists must be converted into a dict (or removed)
Merge pull request #158 from a-ba/master

Fixed malformatted request when using empty list in create_container()