Add option `--safe` to `pcs resource clear` command. If `--safe` is used, pcs should simulate (using simulation functionality of pacemaker) the change first and make sure that no resource (or no specified resources) will be moved after removing the constraint(s). Otherwise the command should fail without committing any changes to the cluster and print out error message with affected resources. Consider adding `--simulate` option as well. If used, pcs should only do simulation of the change and print out its results.