Changed Cheetah exceptions to show all standard error output.

- In case of an unexpected Cheetah related error, collect stdout, stderr
  and backtrace and display them next to the error message
- Remove one obsolete conditional layer according to PR
- Write all available information about an error into results and output
  result on stdout as well as in writing it into the logfile
- Only show stdout/stderr/backtrace if it is available
Add test for Unexpected Error handling.
Factor out the code handling the exception in a separate function for
easier testing and adjusting unit test acordingly.

- Factor out error handling into own function cli.handle_error
- Adjust unit test to raise exception and hand it to handle_error
- Define expected output on stderr as heredoc
Add blank line before Cheetah error message on failing command.

- For symmetry of the error output as suggested in the PR
Make unit test triggering the exception more specific and expect the
machinery error message as string and not as heredoc.
Merge pull request #18 from SUSE/review_140731_dont_cut_error_messages

[Review] Request from 'greygoo' @ 'SUSE/machinery/review_140731_dont_cut_error_messages'