elasticdl/python/elasticdl/__init__.py
from elasticdl.python.elasticdl import layers  # noqa: F401

elasticdl/python/elasticdl/__init__.py
diff --git a/elasticdl/python/elasticdl/__init__.py b/elasticdl/python/elasticdl/__init__.py
index e69de29bb..36a021dd5 100644
--- a/elasticdl/python/elasticdl/__init__.py
+++ b/elasticdl/python/elasticdl/__init__.py
@@ -0,0 +1 @@
+from elasticdl.python.elasticdl import layers  # noqa: F401

No module named 'elasticdl.python.elasticdl.layers' on master
```
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/elasticdl/python/master/main.py", line 28, in <module>
    from elasticdl.python.elasticdl.layers.embedding import Embedding
ModuleNotFoundError: No module named 'elasticdl.python.elasticdl.layers'
```

Seems `layers` directory is not installed to `/usr/local/lib/python3.7/site-packages/elasticdl-develop-py3.7.egg/elasticdl/python/elasticdl` after running `python setup.py install`

Steps to reproduce:

1. In a Python Docker container, clone ElasticDL and run `python setup.py install`
1. remove the cloned source
1. execute a demo job by: `elasticdl train ...`
