Release 20180412 of the `datalab` command line tool.

[ojarjur]

This is a tracking issue for the 20180412 release of the datalab command line tool.

This issue will be used to report the source of the tool, it's changes, and when it is incorporated into the Google Cloud SDK

Source

The commit of the release is 7b586df
A tarball of the CLI tool release can be downloaded by running:

gsutil cp gs://cloud-datalab/datalab-cli-7b586df9e2e26e971cec4bcecb8b8c7669880c10.tgz ./

The following changes are included in this release:

Internal Cleanups:

#1987: Make the tool compatible with Python 3.

[ojarjur]

This went out with the 199.0.0 version of the Cloud SDK