Use exec form of the CMD Dockerfile command in files we scaffold

[karolz-ms]

This is Docker best practice https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#cmd that ensures signals are properly delivered to the main container process and eliminates shell dependency

#2089 highlighted a problem in the Node.js Dockerfiles; there might be other places that need changing

[bwateratmsft]

Looking at the code, we already do this form for Python, CPP, and Ruby. I think only Node and Other need to be changed. Other may not justify it since it is meant as no more than placeholder code to begin with.

[bwateratmsft]

This has been fixed in Docker extension version 1.5.0.