clusterd: add --reexport

`clusterd --reexport` triggers all clusterd daemons to run `mxmount
--reexport-only`. This should be done, when the export groups in
hostconfig were updated.

clusterd/clusterd

@@ -579,6 +579,7 @@ our %UDP_HANDLER=
 	'restart' => \&udp_rx_restart,
 	'flush-gidcache' => \&udp_rx_flush_gidcache,
 	'make-automaps' => \&udp_rx_make_automaps,
+	'reexport'      => \&udp_rx_reexport,
 	'log'  => \&udp_rx_log,
 	'exec' => \&udp_rx_exec,
 	'push' => \&udp_rx_push,
@@ -1089,6 +1090,10 @@ sub udp_rx_make_automaps {
 	system '/sbin/make-automaps';
 }
 
+sub udp_rx_reexport {
+	system '/usr/bin/mxmount --reexport-only';
+}
+
 #----------- tcp mgmt console -----------------------------
 
 our $MGMT_PORT=234;
@@ -1824,6 +1829,7 @@ usage: $0 [options]
   --exec @node cmd [args...] # execute cmd on node
   --flush-gidcache # flush rpc auth.unix.gid cache on all nodes
   --make-automaps  # execute /usr/sbin/make-automaps on all nodes
+  --reexport       # execute /usr/bin/mxmount --reexport-only on all nodes
 
   --lsof=pattern
 
@@ -1851,6 +1857,7 @@ GetOptions
 	'send-restart' => \$options{'send-restart'},
 	'flush-gidcache' => \$options{'flush-gidcache'},
 	'make-automaps' => \$options{'make-automaps'},
+	'reexport'      => \$options{'reexport'},
 	'lsof=s'	=> \$options{'lsof'},
 
 ) or die USAGE;
@@ -1885,6 +1892,10 @@ if (defined $options{'push'}) {
 	sync_cluster_pw() or die "$CLUSTER_PW_FILE: $!\n";
 	$donald_s=new My::Select::INET(Proto=>'udp') or die "$!\n";
 	udp_broadcast_message($donald_s,'make-automaps');
+} elsif (defined $options{'reexport'}) {
+	sync_cluster_pw() or die "$CLUSTER_PW_FILE: $!\n";
+	$donald_s=new My::Select::INET(Proto=>'udp') or die "$!\n";
+	udp_broadcast_message($donald_s,'reexport');
 } elsif (defined $options{'daemon'}) {
 	$options{'kill'} and Donald::Tools::kill_previous_server('clusterd') and sleep 2;