ahg-g: Automated cherry pick of #109442: Correct event registration for multiple scheduler plugins.

JobBuild
3cd291c1
04-13 00:36		 109448
04-13 00:35		 dad7f0a5
04-13 00:33		 unknown
04-13 00:33
pull-kubernetes-conformance-kind-ga-only-parallel 1514248173218959360 1514039709259534336 1514038912442437632
pull-kubernetes-conformance-kind-ipv6-parallel 1514248171906142208 1514039705912479744 1514038911058317312
pull-kubernetes-dependencies 1514248171658678272 1514039696672428032 1514038910873767936
pull-kubernetes-e2e-gce-100-performance 1514248171629318144 1514039695833567232 1514038910852796416
pull-kubernetes-e2e-gce-ubuntu-containerd 1514248171549626368 1514039692478124032 1514038910777298944
pull-kubernetes-e2e-kind 1514248171729981440 1514039700036259840 1514038910940876800
pull-kubernetes-e2e-kind-ipv6 1514248172375904256 1514039707590201344 1514038911599382528
pull-kubernetes-integration 1514248171696427008 1514039698350149632 1514038910907322368
pull-kubernetes-node-e2e 1514248171574792192 1514039706742951936 1514038910806659072
pull-kubernetes-typecheck 1514248171759341568 1514039701709787136 1514038910966042624
pull-kubernetes-unit 1514248174053625856 1514039710098395136 1514038913272909824
pull-kubernetes-verify 1514248171818061824 1514039702548647936 1514038910999597056
pull-kubernetes-verify-govet-levee 1514248171851616256 1514039704662577152 1514038911028957184