tests: Enable RSA SHA1 certs for testing against older OpenSSH
The OpenSSH 7.4 or 7.6 in Ubuntu and CentOS 7 does not support SHA2
RSA certificates and libssh automatically falls back to SHA1, which
is not allowed by default.
Signed-off-by: Jakub Jelen <email@example.com>
Reviewed-by: Anderson Toshiyuki Sasaki <firstname.lastname@example.org>
(cherry picked from commit db948bdac87ec9ad190cadbd9444902e5fbe691a)