support "mogadm device (list|summary) --hostname=..."

For large clusters with many hosts/devices, it is often helpful
to only show the devices for a given host.

This functionality is useful for me since "mogadm device list"
output is not grep-friendly.

mogadm

@@ -84,13 +84,15 @@ my $usage = {
                 args => "[opts]",
                 opts => {
                     "--all"  => "Include dead devices in list.",
+                    "--hostname=s" => "Limit results to a given host.",
                 },
             },
             summary => {
                 des => "List the summary of devices, for each host.",
                 args => "[opts]",
                 opts => {
                     "--status=s"  => "Devices of status A. Defaults to 'alive,readonly'",
+                    "--hostname=s" => "Limit results to a given host.",
                 },
             },
             add => {
@@ -806,9 +808,13 @@ sub cmd_device_list {
 
     my $devs = devices();
     fail_text('no_devices') unless $devs;
+    my $hostname = $args->{hostname};
 
     foreach my $hostid (sort keys %$hosts) {
         my $host = $hosts->{$hostid};
+        if (defined $hostname && $hostname ne $host->{hostname}) {
+            next;
+        }
         print "$host->{hostname} [$hostid]: $host->{status}\n";
 
         printf "%6s  %-10s %7s %7s %7s\n", '', '', 'used(G)', 'free(G)', 'total(G)';
@@ -830,6 +836,7 @@ sub cmd_device_list {
 
 sub cmd_device_summary {
     my $args = shift;
+    my $hostname = $args->{hostname};
     my %show_state;
     $show_state{$_} = 1 foreach split(/,/, ($args->{status} || "alive,readonly"));
 
@@ -842,6 +849,9 @@ sub cmd_device_summary {
     printf "%-15s %6s %7s  %8s %8s %8s %8s\n", 'Hostname', 'HostID', 'Status', 'used(G)', 'free(G)', 'total(G)', '%Used';
     foreach my $hostid (sort keys %$hosts) {
         my $host = $hosts->{$hostid};
+        if (defined $hostname && $hostname ne $host->{hostname}) {
+            next;
+        }
         my ($total,$used) = (0, 0);
 
         foreach my $devid (sort keys %{$devs->{$hostid} || {}}) {