Resolving issue - #35 - Error display when docker-build perform

[BabaYaga1221]

The issue of suppressed output when encountering build errors in the docker_build function has been resolved by modifying the code to handle errors by capturing and printing the output message instead of suppressing it. The modified code now allows users to see the full error message and easily diagnose the issue.
Fixes #35
@tfoote

[tfoote]

Thanks for looking at this. However it gives the code backtrace from the code path and not the error from the underlying command that I'd like to expose.

You can see if you run rocker --user hello-world --noex that it still prints Exception: Build failed: no more output and success not detected with the backgrace

What it should print is the error from the build step.
If you run it after the above and substitute the last image id into this command docker run -ti --rm 4939e01e77c4

You'll see the useful error: docker: Error response from daemon: unable to find user root: no matching entries in passwd file. Which is what should be visible to the user as that's the underlying error not the backtrace.

[BabaYaga1221]

@tfoote Would you like to review the code to see if the build errors can be traced back more clearly?

[tfoote]

It does print the build commands.

Exception: Build failed: Step 1/7 : FROM hello-world
 ---> feb5d9fea6a5
Step 2/7 : USER root
 ---> Using cache
 ---> 4939e01e77c4
Step 3/7 : RUN if ! command -v sudo >/dev/null; then       apt-get update       && apt-get install -y sudo       && apt-get clean;     fi
 ---> Running in 5a5af0f73975

But it doesn't print the underlying error so that the user can know what failed.

And secondly, just throwing the exception and printing the build output is not a good user experience. The exception should be caught and helpful context should be supplied to the user about what was being tried to run, what the error was, and hopefully how they can reproduce it for debugging.

[BabaYaga1221]

hi @tfoote, I apologize for being inactive on this PR, but, can you please help with what should I change?
The last time when I work on it, I only ended only one solution that I should manually describe the error and provide particular steps to resolve it.

[tfoote]

You need to catch the underlying build error output. And then present what was attempted as well as the error output for the user to understand what failed so they can then fix the problem themselves.