infrabox does not check environment

[steinemann]

Describe the bug
I installed infrabox with pip and simply started the HelloWorld example.
Unfortunately it fails saying that docker does not understand the parameter --cpus

** Resolution**
I had to update my docker installation from 12.x to a newer one.

Expected behavior
A clear information that the installed docker version is too old, would be more speaking than
just a simple python error.
Also the documentation should be updated.

[ib-steffen]

Moved to CLI repo