test: wait till nic edit button is loaded

To avoid accidentally misclicking the edit button which rendering is
depended on some I/O to succeed.

Author: jelly

test/check-machines-nics

@@ -228,6 +228,8 @@ class TestMachinesNICs(machineslib.VirtualMachinesCase):
         def plugAndUnplugNICs():
             mac_address = b.text("#vm-subVmTest1-network-1-mac")
 
+            # Edit dialog loads asynchronous, wait on it to load first so we don't misclick.
+            b.wait_visible("#vm-subVmTest1-network-1-edit-dialog:not(:disabled)")
             b.wait_in_text("#vm-subVmTest1-network-1-state", "up")
             b.wait_in_text("#vm-subVmTest1-iface-1-unplug", "Unplug")