Some type of BMCs don't support an IPMI option that disable the
behavior of boot device timeout, which makes them never get booted
from PXE.
This patch extends the fix [1] by adding a configuration option,
which provides the default ipmi behavior.
[1] https://review.openstack.org/#/c/616053
Additionally revising the variable/setting names based upon review
feedback and discussion that took place during the 20181210 weekly
ironic team meeting.
Change-Id: Ie049bbaf45aeab54c1272d1d561c5a6ca00dc34a
Story: 2002977
Task: 22985
d379357cad