Most bootstrap actions use the run_once flag to run on a single host
as they typically involve service-global operations such as database
syncs. The ironic_pxe container bootstrap is different, as it copies
pxelinux files into the ironic_pxe Docker volume. This should be done
on all hosts but currently is only done on one host.
This change performs the ironic_pxe bootstrap on all hosts in the
ironic-pxe group.
Change-Id: Iffd34e6ff26a0ba5140e5d477418cc8aebcdac62
Closes-Bug: #1667153