virsh: Add a completer for domifaddr --source parameter.

The command `domifaddr` can use three different sources to grab IP
address of a Virtual Machine: lease, agent and arp. This parameter does
not have a completer function to return source options.

Signed-off-by: Julio Faracco <jcfaracco@gmail.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>

tools/virsh-completer-domain.h

@@ -53,3 +53,8 @@ char ** virshDomainDeviceAliasCompleter(vshControl *ctl,
 char ** virshDomainShutdownModeCompleter(vshControl *ctl,
                                          const vshCmd *cmd,
                                          unsigned int flags);
+
+char **
+virshDomainInterfaceAddrSourceCompleter(vshControl *ctl,
+                                        const vshCmd *cmd,
+                                        unsigned int flags);