Handle Interrupt exceptions better

Before this commit, pressing Ctrl+C when executing a command action
resulted into output like this:

  [1/1] Processing testsuite:
    * Creating result directory...
  ^C    ERROR: Creating result directory failed.

This commit moves the Interrupt exception processing above the code that
print the error message. The output now looks like this:

  [1/1] Processing testsuite:
    * Creating result directory...
  ^C
Handle SystemExit explicitly in toplevel exception handler

Without this, YCP Killer printed red "exit" at the end of the output
when any command which uses CLI#report_results failed (e.g. when trying
to convert an YCP file with a syntax error).
Colorize result counters
Unify how exceptions are printed
Merge pull request #600 from yast/error-handling-cleanups

[Review] Request from '' @ 'yast/ycp-killer/error-handling-cleanups'