Comment 4 for bug 1053312

I found plug operation to be actually potentially called twice - at least for the libvirt virt driver

spawn --> to_xml --> get_guest_config --> plug (used for adding device info to VM configuration)
spawn --> _create_domain_and_network --> plug_vifs --> plug (the "real" plug action)

Therefore we need the call to be idempotent, as stated by Vish, and we should take this patch.

However, this still do not quite explain why the behaviour is apparently not deterministic (or at least we have users confirming it works and other users say it doesn't work, and finally also users saying it works at times!)

See bug 1053457 as potentially related