fix SSL cert monitoring on LDAP servers

replace the older check_cert check which currently
fails with the other existing plugin for this purpose,
check_ssl_cert which we also use for the monitoring of
certs on the main cluster nginx'es

but, that one did not have an option for the port
and a specific CA yet. just make a new specific checkcommand
for the LDAP servers instead of touching all existing
cert monitoring

Change-Id: I52c19555706fe85b4a7837c181e761e44c3b22bd