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

JobBuild
d2596d42
04-13 16:59		 109466
04-13 16:52		 583e1f80
04-13 16:50
pull-kubernetes-conformance-kind-ga-only-parallel 1519621906385342464 1519572352847843328 1514287028827590656 1514284855125348352
pull-kubernetes-conformance-kind-ipv6-parallel 1514287027162451968 1514284853799948288
pull-kubernetes-dependencies 1519621906167238656 1519572352122228736 1514287015317737472 1514284853590233088
pull-kubernetes-e2e-gce-100-performance 1519621906129489920 1519572352084480000 1514287023798620160 1514284853556678656
pull-kubernetes-e2e-gce-ubuntu-containerd 1519621906041409536 1519572352000593920 1514287012813737984 1514284853485375488
pull-kubernetes-e2e-kind 1519621690005393408 1519572352206114816 1514287018765455360 1514284853657341952
pull-kubernetes-e2e-kind-ipv6 1519621906351788032 1519572352357109760 1514287027997118464 1514284854290681856
pull-kubernetes-integration 1519621906204987392 1519572352172560384 1514287017083539456 1514284853627981824
pull-kubernetes-node-e2e 1519621906074963968 1519572352034148352 1514287013640015872 1514284853510541312
pull-kubernetes-typecheck 1519621906242736128 1519572352239669248 1514287021697273856 1514284853695090688
pull-kubernetes-unit 1519621906880270336 1519572353674121216 1514287030513700864 1514284855964209152
pull-kubernetes-verify 1519621906272096256 1519572352277417984 1514287022120898560 1514284853732839424
pull-kubernetes-verify-govet-levee 1519621906314039296 1519572352319361024 1514287026319396864 1514284853762199552