Add a test "uitest"

It tests both the use of UI_METHOD (through the apps/apps.h API) and
wrapping an older style PEM password callback in a UI_METHOD.

Replace the earlier UI test with a run of this test program

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2204)