This fixes an issue where the build output for the "Steps" would look like:
```
Step 1: RUN echo hi echo hi
```
instead of
```
Step 1: RUN echo hi
```
Also, I noticed that there were no checks to make sure invalid Dockerfile
cmd flags were caught on cmds that didn't use cmd flags at all. They would
have been caught on the cmds that had flags, but cmds that didn't bother
to add a new code for flags would have just ignored them. So, I added
checks to each cmd to flag it.
Added testcases for issues.
Signed-off-by: Doug Davis <dug@us.ibm.com>
Upstream-commit: 08b7f30fcd050244026098673b19700485308b5a
Component: engine
ba0c92d010