fixes #2055 - add rubyipmi dependency for BMC support

http://ci.theforeman.org/job/packaging_build_matrix_rpm/56/
http://koji.katello.org/koji/taskinfo?taskID=42101
http://koji.katello.org/koji/taskinfo?taskID=42102

rubyipmi's not in our repos yet, waiting for a change in the koji config first for the comps location (to foreman-packaging) to pick it up.