Booting instances from PXE is Ironic legacy. It's not supported with network separation, and has other known problems. TripleO uses local boot by default. Upstream RFE: https://bugs.launchpad.net/ironic/+bug/1619339
Proposing for 13.
*** Bug 1490182 has been marked as a duplicate of this bug. ***
This is close, we just need to figure out upstream CI (cirros does not have grub2)