Increase concurrency for ironic jobs to 4
Increase concurrency for ironic jobs to 4

Nova has fixed issue with rescheduling [0] and it was backported to
Ocata [1].

This updates concurrency to 4 for the following jobs. The timing
benefits may be found in temp patch [2]

  * ironic-standalone: previous concurrency 2, approx exec 37-45min
                       current concurrency 4, approx 28-35min
  * ironic-multinode: previous concurrency 2, approx exec 81-83min
                      current concurrency 4, approx exec 59-80min
  * ironic-grenade-multinode: previous concurrency 1, approx exec
                              120-150min
                              current concurrency 4, approx exec
                              85-110min

[0] https://bugs.launchpad.net/nova/+bug/1671648
[1] https://review.openstack.org/#/c/446262/
[2] https://review.openstack.org/#/c/413499/

Change-Id: Ibda036f4542a84e26033adbc7268dbd2d37c20f5

openstack-infra/project-config,openstack-infra/project-config