Add package ca-certificates to slapd base image

Add the ca-certificates package to the slapd base image so that any
clients or client libraries that need to call out, such as syncrepl
clients, can properly check server TLS certificates and do
ldaps://.

comanage-registry-slapd-base/Dockerfile

@@ -20,6 +20,7 @@ FROM debian:jessie
 
 RUN apt-get update \
     && DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y \
+        ca-certificates \
         ldap-utils \
         slapd \
     && cp -a /var/lib/ldap /var/lib/ldap.dist \