mussel,test: replace common variables with helper_vars.sh.
mussel,test: api_version -> DCMGR_API_VERSION.
mussel,test: host -> DCMGR_HOST.
mussel,test: port -> DCMGR_PORT.
mussel,test: base_uri -> DCMGR_BASE_URI.
mussel,test: remove unused api_version.
mussel,test: beautify code.