CI: undercloud idempotency step fails because of out of memory

Last two periodic ovb-nonha jobs failed because of out of memory on second undercloud installation (UNDERCLOUD_IDEMPOTENT)

016-12-21 07:49:24.738348 | 2016-12-21 07:49:05,005 INFO: Error: /Stage[main]/Neutron::Agents::Ml2::Ovs/Neutron::Plugins::Ovs::Bridge[ctlplane:br-ctlplane]/Vs_bridge[br-ctlplane]: Could not evaluate: Cannot allocate memory - fork(2)
2016-12-21 07:49:24.738416 | 2016-12-21 07:49:11,050 INFO: Error: /Stage[main]/Xinetd/Service[xinetd]: Could not evaluate: Cannot allocate memory - fork(2)
2016-12-21 07:49:24.738490 | 2016-12-21 07:49:12,756 INFO: Error: /Stage[main]/Zaqar::Server/Service[openstack-zaqar]: Could not evaluate: Cannot allocate memory - fork(2)
2016-12-21 07:49:24.738578 | 2016-12-21 07:49:12,761 INFO: Error: /Stage[main]/Main/Zaqar::Server_instance[1]/Service[openstack-zaqar@1]: Could not evaluate: Cannot allocate memory - fork(2)
2016-12-21 07:49:24.738653 | 2016-12-21 07:49:12,762 INFO: Notice: /Stage[main]/Zaqar::Deps/Anchor[zaqar::service::end]: Dependency Service[openstack-zaqar] has failures: true
2016-12-21 07:49:24.738737 | 2016-12-21 07:49:12,762 INFO: Notice: /Stage[main]/Zaqar::Deps/Anchor[zaqar::service::end]: Dependency Service[openstack-zaqar@1] has failures: true
2016-12-21 07:49:24.738816 | 2016-12-21 07:49:12,763 INFO: Warning: /Stage[main]/Zaqar::Deps/Anchor[zaqar::service::end]: Skipping because of failed dependencies
2016-12-21 07:49:24.738929 | 2016-12-21 07:49:13,437 INFO: Notice: /Stage[main]/Keepalived::Config/Concat[/etc/keepalived/keepalived.conf]/File[/etc/keepalived/keepalived.conf]/content: content changed '{md5}522ab27809e9957258aebb46904ef7b4' to '{md5}bfcb24c448663cb03980a1bed0308069'
2016-12-21 07:49:24.739001 | 2016-12-21 07:49:13,445 INFO: Error: /Stage[main]/Keepalived::Service/Service[keepalived]: Could not evaluate: Cannot allocate memory - fork(2)
2016-12-21 07:49:24.739227 | 2016-12-21 07:49:13,446 INFO: Error: /Stage[main]/Keepalived::Service/Service[keepalived]: Failed to call refresh: Cannot allocate memory - fork(2)
2016-12-21 07:49:24.739348 | 2016-12-21 07:49:13,446 INFO: Error: /Stage[main]/Keepalived::Service/Service[keepalived]: Cannot allocate memory - fork(2)
2016-12-21 07:49:24.739644 | 2016-12-21 07:49:14,457 INFO: Error: Failed to apply catalog: Cannot allocate memory - fork(2)

http://logs.openstack.org/periodic/periodic-tripleo-ci-centos-7-ovb-nonha/287dfa2/console.html
http://logs.openstack.org/periodic/periodic-tripleo-ci-centos-7-ovb-nonha/f2341c3/console.html