Document returning False in test=True mode
Document returning False in test=True mode

Currently, in test mode states always return None even on failure.
This masks failed states in highstate output,
which instead just look like they are going to make changes.

In some cases states can determine if they will fail even on a dry run,
e.g., if an API call to a service to determine the state of a
resource fails due to invalid credentials or a missing parameter.

In these cases, allow returning a result of False even in dry runs
to enable catching more errors at testing time.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt