Handle internal err, report issue with empty CODEOWNERS or git dirty state

[mszostok]

Description

Changes proposed in this pull request:

• Handle internal checks errors
  Previously they were only logged, now there are printed to check results and proper exit code is also set.
  Instead of:

  time="2022-02-27T09:21:01Z" level=error msg="while executing checker [Experimental] Not Owned File Checker: 1 error occurred:\n\t* fatal: No pathspec was given. Which files should I remove?\n: command \"xargs\": exit status 123\n\n" service="check:runner"
  

  We have:

  ==> Executing [Experimental] Not Owned File Checker (23.312587ms)
      [Internal Error] No pathspec was given. Which files should I remove?\n: command \"xargs\": exit status 123
  
  1 check(s) executed, 1 failure(s)
  exit status 3
  

• Report issue with empty CODEOWNERS

  ==> Executing [Experimental] Not Owned File Checker (23.312587ms)
      [err] The CODEOWNERS file is empty. The files in the repository don't have any owner.
  
  1 check(s) executed, 1 failure(s)
  exit status 3
  

• Report or git dirty state

  ==> Executing [Experimental] Not Owned File Checker (23.312587ms)
      [err] git state is dirty: commit all changes before executing this check
  
  1 check(s) executed, 1 failure(s)
  exit status 3
  

Related issue(s)

Fix #126