mon: implement "fs [new|rm|ls]"

Signed-off-by: John Spray <john.spray@redhat.com>
test: add "fs [new|ls|rm]" argparse tests

Signed-off-by: John Spray <john.spray@redhat.com>
qa: update 'newfs' -> 'fs new'

Signed-off-by: John Spray <john.spray@redhat.com>
vstart: update from newfs to 'fs new'

Signed-off-by: John Spray <john.spray@redhat.com>