After installing chrony, we need to update the selection to match
the initial setting in the chrony.conf file.

If no ntp service is installed, display the default "pool.ntp.org".

drakclock can install chrony, so the ntpd and ntp_conf strings
provided by the imezone module should be dynamic, not static.

drakclock only supports selecting a server pool, not individual servers,
so use the "pool" directive instead if the "server" directive. Rename
the subroutines in timezone.pm for clarity.

ntpsec overrides /etc/ntp.conf with settings found in /etc/ntp.d/, so
we need to read/write /etc/ntp.d/use-pool.

Both chrony and ntpsec support the iburst option, so we can write that
unconditionally.

The $mode variable is always set to 0 when starting the drakclock, so
the checkbox was unchecked by default.

Now if the ntpd service is started we check it

ntpq in drakclock.
MGA#22850

Depending on machine speed/slowness, signals will not be fired in the
order expected and Repaint() will be called before global variable
$cairo is set by draw().

This can be reproduced by making $timer to happens much faster than
every 120ms so that it happens before the first call to draw()

This workaround fix the bug introduced in commit 1a30f422b41250e338d2c1d209aec1b64204c8e0

But it would probably be saner to get rid of the $cairo global variable
and to create a Cairo context in every Repaint() caller instead...