Remove unused stub
replace fail <string> by fail Errors::...
add contributing file
Merge pull request #152 from ggiamarchi/error_handling

replace fail <string> by fail Errors::...
Catch unhandled exception and prints contribution message

Fix #115
Handle global exception in abstract_command
add the same behaviour in abstract action than in abstract command
fix merge errors
Remove redondant rubocop:disable
Make WaitForServerToBeAccessible inherits from AbstractAction
Known errors must not be catched
Introduce Errors::Timeout

Now it is important that all expected exceptions
inherit from VagrantOpenstackError