ipaserver: Add support for 4.7 (4.6.90-pre2)

With IPA 4.7 bigger changes have been introduced

Changes:
- Use of timeconf and chrony instead of ntpconf and ntpd.
- New IPAChangeConf (not used in ipaserver modules)
- New check_ldap_conf form ipaclient.install.client
- custodia instance needed for ca and kra
- no_ntp defaults to yes for client installation part
- A new option ntp_pool has been introduced (set to None).