virsh: Fix *-event error string

When using
virsh net-event non-existing-net
the error message says that 'either --list or event type is required'
This is misleading as 'virsh net-event $valid-event-type' is not going
to work either. What is expected is 'virsh net-event --event
$valid-event-type'

This commit fixes the string in pool-event, nodedev-event, event, and
net-event.

tools/virsh-domain.c

@@ -12694,7 +12694,7 @@ cmdEvent(vshControl *ctl, const vshCmd *cmd)
         }
     } else if (!all) {
         vshError(ctl, "%s",
-                 _("one of --list, --all, or event type is required"));
+                 _("one of --list, --all, or --event <type> is required"));
         return false;
     }
 

tools/virsh-network.c

@@ -1238,7 +1238,7 @@ cmdNetworkEvent(vshControl *ctl, const vshCmd *cmd)
     if (vshCommandOptStringReq(ctl, cmd, "event", &eventName) < 0)
         return false;
     if (!eventName) {
-        vshError(ctl, "%s", _("either --list or event type is required"));
+        vshError(ctl, "%s", _("either --list or --event <type> is required"));
         return false;
     }
     if ((event = virshNetworkEventIdTypeFromString(eventName)) < 0) {

tools/virsh-nodedev.c

@@ -903,7 +903,7 @@ cmdNodeDeviceEvent(vshControl *ctl, const vshCmd *cmd)
     if (vshCommandOptStringReq(ctl, cmd, "event", &eventName) < 0)
         return false;
     if (!eventName) {
-        vshError(ctl, "%s", _("either --list or event type is required"));
+        vshError(ctl, "%s", _("either --list or --event <type> is required"));
         return false;
     }
 

tools/virsh-pool.c

@@ -2057,7 +2057,7 @@ cmdPoolEvent(vshControl *ctl, const vshCmd *cmd)
     if (vshCommandOptStringReq(ctl, cmd, "event", &eventName) < 0)
         return false;
     if (!eventName) {
-        vshError(ctl, "%s", _("either --list or event type is required"));
+        vshError(ctl, "%s", _("either --list or --event <type> is required"));
         return false;
     }