Replace 'echo -n' with 'printf' in tests/t_lpback.sh

Replace 'echo -n' with 'printf' in tests/t_lpback.sh

"echo -n" is inherently less portable than printf, so the tests look
ugly on (at least) OpenSolaris/Illumos on AIX.

Add a blank at the end of the tls-crypt-v2 messages, so it has the
same look as the cipher messages ("... OK").

Reported-by: mnowak on Trac
Trac: #1196

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Antonio Quartulli <a@unstable.cc>
Message-Id: <20200909130024.24264-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20930.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 81f9bb3a2ff9a3b0f5a1bdbac1d0daf38747ae7b)