Failed to allocate network error when creating vms

Issue

• Randomly getting "Failed to allocate network"
• Cisco ACI
• BuildAbortException: Build of instance XXXX aborted: Failed to allocate the network(s), not rescheduling.

• Timeout of ~ 300 seconds between events:

  2018-07-13 20:20:00.136 561173 DEBUG nova.compute.manager [XXXX] Preparing to wait for external event network-vif-XXXXX prepare_for_instance_event /usr/lib/python2.7/site-packages/nova/compute/manager.py:328
  2018-07-13 20:25:01.501 561173 WARNING nova.virt.libvirt.driver [XXX - - -] [instance: XXX] Timeout waiting for vif plugging callback for instance XXX