3.0: Make console option parsers mergable/combinable

Resolves https://github.com/cakephp/cakephp/issues/5231

Make console option parsers mergable/combinable
It is copy-and-paste from 3 other places where this check was exactly the same, e.g.
- https://github.com/cakephp/cakephp/blob/3.0/src/Console/ConsoleOptionParser.php#L282
- https://github.com/cakephp/cakephp/blob/3.0/src/Console/ConsoleOptionParser.php#L333
- https://github.com/cakephp/cakephp/blob/3.0/src/Console/ConsoleOptionParser.php#L400