Refactor check_docker()
Refactor check_docker()

This partially reverts commit d680ab6e30077b7188e5b4b21177f692f3cdddf3.
Use subprocess.check_call() instead of os.system().
Redirect process' stdout and stderr to /dev/null.

jberci/resolwe,jberci/resolwe,genialis/resolwe,genialis/resolwe