Release v0.2.0-rc2

• Refactor the common modules between elasticdl main package and elasticdl_client.
• Add more default value for ElasticDL command arguments. User can submit an ElasticDL job with shorter commands.
• BUGFIX: elasticdl_ps may be not found while building with various base images.

Release v0.2.0-rc1

Release three pip packages in https://pypi.org/

• elasticdl: https://pypi.org/project/elasticdl/
• elasticdl_client: https://pypi.org/project/elasticdl-client/
• elasticdl_preprocessing: https://pypi.org/project/elasticdl-preprocessing/