ipaclient: New module ipaclient_setup_ntp, dropped ipaclient_ntp setting

The new module ipaclient_setup_ntp to configure and sync time with the NTP
server has been added. The irregular setting ipaclient_ntp has been removed.

The ipaclient_setup_ntp module is using either the new sync_time call or
for compatibility with older FreeIPA versions synconce_ntp.

The reference for ipaclient_ntp in REPLICA.md has been removed also.

This also fixes #55.