Add flask. (Kaggle#946)

- Also added tests to prevent regression.

flask was removed from the base image we use:

```
rosbo@rosbo:~$ docker run -it --rm gcr.io/deeplearning-platform-release/base-cpu:m46 pip show flask
Name: Flask
Version: 1.1.2
Summary: A simple framework for building complex web applications.
Home-page: https://palletsprojects.com/p/flask/
Author: Armin Ronacher
Author-email: armin.ronacher@active-4.com
License: BSD-3-Clause
Location: /opt/conda/lib/python3.7/site-packages
Requires: Werkzeug, itsdangerous, click, Jinja2
Required-by:
rosbo@rosbo:~$ docker run -it --rm gcr.io/deeplearning-platform-release/base-cpu:m61 pip show flask
WARNING: Package(s) not found: flask
```

Add flask. (Kaggle#946)

- Also added tests to prevent regression.

flask was removed from the base image we use:

```
rosbo@rosbo:~$ docker run -it --rm gcr.io/deeplearning-platform-release/base-cpu:m46 pip show flask
Name: Flask
Version: 1.1.2
Summary: A simple framework for building complex web applications.
Home-page: https://palletsprojects.com/p/flask/
Author: Armin Ronacher
Author-email: armin.ronacher@active-4.com
License: BSD-3-Clause
Location: /opt/conda/lib/python3.7/site-packages
Requires: Werkzeug, itsdangerous, click, Jinja2
Required-by:
rosbo@rosbo:~$ docker run -it --rm gcr.io/deeplearning-platform-release/base-cpu:m61 pip show flask
WARNING: Package(s) not found: flask
```

Fix theano test (Kaggle#941)

http://b/178107003

Fix theano test (Kaggle#941)

http://b/178107003

Post jenkins updates to Mattermost (Kaggle#938)

http://b/174603325

Post jenkins updates to Mattermost (Kaggle#938)

http://b/174603325

Simplified Cloud AI API integration. (Kaggle#932)

* Cloud Translation, Natural language, Vision,
Video intelligence GCP integrations.

Merge pull request Kaggle#913 from Kaggle/add-xgboost-version-regress…

…ion-test

Add xgboost version regression test.

Merge pull request Kaggle#913 from Kaggle/add-xgboost-version-regress…

…ion-test

Add xgboost version regression test.

Merge pull request Kaggle#907 from marketneutral/master

Add datatable by h2oai