Produce a meaningful error message if --daemon gets in the way of asking for passwords.

Produce a meaningful error message if --daemon gets in the way of asking for passwords.

With the --daemon / SSL init reordering in da9b292733, we fail if we
daemonize first and then try to ask for a private key passphrase (or,
for that matter, username+password if --auth-nocache is set) - but
no meaningful error message was printed, instead depending on operating
system and library versions, either we looped around "ssl init failed"
or died with an unspecified "fatal error".

So: check if get_user_pass_cr() is called in a context that needs
"from_stdin", but both stdin and stderr are not connected to a tty
device (which getpass() needs).  In that case, print a meaningful
error message pointing to --askpass, and die.

Trac #574 and #576

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1436814607-16707-1-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9916
(cherry picked from commit 079e5b9c13bf81d7afc6f932b5417d2f08f8e64b)