mogadm: include drain devices by default in summary

drain devices are still usable to clients, so it probably makes
sense to include this in the default output of "mogadm device summary"
(especially given the drain change in 2.40)

Not including drain devices by default confused me at first, so
perhaps it may be confusing to others.

mogadm

@@ -91,7 +91,7 @@ my $usage = {
                 des => "List the summary of devices, for each host.",
                 args => "[opts]",
                 opts => {
-                    "--status=s"  => "Devices of status A. Defaults to 'alive,readonly'",
+                    "--status=s"  => "Devices of status A. Defaults to 'alive,readonly,drain'",
                     "--hostname=s" => "Limit results to a given host.",
                 },
             },
@@ -845,7 +845,7 @@ sub cmd_device_summary {
     my $args = shift;
     my $hostname = $args->{hostname};
     my %show_state;
-    $show_state{$_} = 1 foreach split(/,/, ($args->{status} || "alive,readonly"));
+    $show_state{$_} = 1 foreach split(/,/, ($args->{status} || "alive,readonly,drain"));
 
     my $hosts = hosts();
     fail_text('no_hosts') unless $hosts;