Description of problem: Activation stops silently if --filestore or --bluestore is not explicitly used


How reproducible: Always


Steps to Reproduce:
1. ceph-volume lvm activate $ID $FSID

Actual results: No output, exit status code of 0


Expected results: Activation succeeds like when using --bluestore


Additional info: This is basically because this piece of code:

        if args.bluestore is None and args.filestore is None:
            args.bluestore = True

Should be checking for false-ish values, not None. `args.bluestore` is False, as well as args.filestore