Fixed error whilst using rak8s with Raspbian Buster

[sbaeurle]

Fixed error whilst using master branch with Raspbian Buster

Description

Whilst bootstrapping to newly installed PI3s with Raspbian Buster installed I encountered the following errors:

• get-docker.sh is not working correctly, since the install script checks for the os id and raspbian buster is apparently not listed.
• after adding the kubernetes apt repository the apt-get update step was lost.

Solutions:

• Added the newest revision of the get-docker.sh from https://get.docker.com
• readded the apt-get update step from the 0.2.2 release

Testing

I've tested the my changes with a PI cluster with 1 master and 2 worker nodes. The bootstrapping went flawlessly and the kubernetes cluster is up and running.

Issue Number

I did not open an issue for this fixes

[sbaeurle]

i downloaded the script from https://get.docker.com