Use recommended EXEC form of commands

[bwateratmsft]

Fixes #2090

NOTE: the "Other" scaffolding still uses the other form (CMD /usr/games/fortune -a | cowsay). I don't think there's value in changing that for two reasons--

1. The "Other" Dockerfile is little more than a demonstration of how Dockerfiles look.
2. The intended behavior of the image does not work when using the EXEC form + sh, -c. It is supposed to output a random bit of text (the output from /usr/games/fortune) and put it into a text box being spoken by the Docker whale (the pipe into cowsay). If the EXEC form is used, nothing is output to the terminal doing the docker run; instead the output is just into the container itself.

[karolz-ms]

Regarding the "Other" Dockerfile, the EXEC form works for me:

FROM docker/whalesay:latest
LABEL Name=scaffold Version=0.0.1
RUN apt-get -y update && apt-get install -y fortunes
CMD ["sh", "-c", "/usr/games/fortune -a | cowsay"]

$ docker run --rm -it  scaffold:latest
 ______________________________________ 
/ "Intelligence without character is a \
| dangerous thing."                    |
|                                      |
\ -- G. Steinem                        /
 -------------------------------------- 
    \
     \
      \     
                    ##        .            
              ## ## ##       ==            
           ## ## ## ##      ===            
       /""""""""""""""""___/ ===        
  ~~~ {~~ ~~~~ ~~~ ~~~~ ~~ ~ /  ===- ~~~   
       \______ o          __/            
        \    \        __/             
          \____\______/   

(tried on a Mac)

[karolz-ms]

LGTM. Consider changing the "Other" case too for consistency; it seems to be working as expected.

[bwateratmsft]

Regarding the "Other" Dockerfile, the EXEC form works for me:

Weird, I did exactly what you're doing and it did not work for me. I'll try again.

[bwateratmsft]

Regarding the "Other" Dockerfile, the EXEC form works for me:

Weird, I did exactly what you're doing and it did not work for me. I'll try again.

Yup, this time it's working. shrug