ipaclient: Support sync_time changes of 4.8.0

sync_time is not using options anymore, but has two new arguments. These
are ntp_servers and ntp_pool. The options argument is not used anymore.

This requires to use inspect on sync_time to be able to detect if the old
or the new function is available.

The call for get_time_source has been added, but is documented out as the
call is only useful in interactive mode.

ipaclient_test now returns ntp_servers and ntp_pool, which are then used
for ipaclient_setup_ntp.