Make 'Broken' workers show as 'Unavailable' instead

This commit displays "Broken" workers as instead "Unavailable",
as the previous wording was e.g. not including workers which where
unavailable due to 'too high load'.
For the same reason the 'Error' title of the worker states hover popup is replaced with
'Details' and the 'too high load' output is enhanced.

Related Ticket: https://progress.opensuse.org/issues/164084

lib/OpenQA/Worker.pm

@@ -767,7 +767,8 @@ sub _check_system_utilization (
     return undef unless $threshold && @$load >= 3;
     # look at the load evolution over time to react quick enough if the load
     # rises but accept a falling edge
-    return "The average load (@$load) is exceeding the configured threshold of $threshold."
+    return
+"The average load (@$load) is exceeding the configured threshold of $threshold. The worker will temporarily not accept new jobs until the load is lower again."
       if max(@$load) > $threshold && ($load->[0] > $load->[1] || $load->[0] > $load->[2] || min(@$load) > $threshold);
     return undef;
 }

templates/webapi/admin/workers/worker_status.html.ep

@@ -15,7 +15,7 @@
         )
     %>
 % } elsif ($worker->{status} eq 'broken') {
-    Broken <%= help_popover(Error => $worker->{error}) %>
+    Unavailable <%= help_popover(Details => $worker->{error}) %>
 % } elsif ($worker->{alive}) {
     Idle
 % } else {