Convenience function for iterating while the result is Ok

Convenience function for iterating while the result is Ok

For a function f :: a -> GenericResult a, iterate it (in the sense of the
monad), until the result is Bad; return the list of values occurred.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>