Beaker's ipmilan power script uses -i to pass the power address to fence_ipmilan, but that option is apparently deprecated and was removed entirely in the 4.0 release of fence-agents. The script should be using -a to specify the address instead. RHEL6 recently rebased to 4.0 and so this broke the ipmilan power script. (Bug 1254046 is for the regression in RHEL6 fence-agents.)
http://gerrit.beaker-project.org/4349
Beaker 21.1 has been released.