move command validating up into CLI [#82004144]

Signed-off-by: Eric Tsiliacos <etsiliacos@pivotal.io>
treat flags as commands #[82004144]

Signed-off-by: Eric Tsiliacos <etsiliacos@pivotal.io>
extract and use command validator [#82004144]

Signed-off-by: Eric Tsiliacos <etsiliacos@pivotal.io>