Fix ntpd config on clients.

https://fedorahosted.org/freeipa/ticket/4094
ntpconf: remove redundant comment

https://fedorahosted.org/freeipa/ticket/4094
Get original entry state from LDAP in LDAPUpdate.
Convert remaining installer code to LDAPEntry API.
Convert remaining update code to LDAPEntry API.
Convert remaining test code to LDAPEntry API.
Raise an exception when legacy LDAP API is used.
Convert remaining frontend code to LDAPEntry API.