library/ipadiscovery: Add time synchronization calls

Attempt to sync time if on_master is not set and no_ntp is not set: At
first with given or dicovered time servers. If no ntp servers have been
given or discovered, then with the ipa server.

New parameters:
  on_master:
    description: IPA client installation on IPA server
    required: false
    default: false
    type: bool
    default: no
  ntp_servers:
    description: List of NTP servers to use
    required: false
    type: list
    default: []
  no_ntp:
    description: Do not sync time and do not detect time servers
    required: false
    default: false
    type: bool
    default: no

The ntp_servers output parameter is now always an empty list if on_master
or no_ntp is set.