fix service account names in the instructions for OpenShift (#1083)
fix service account names in the instructions for OpenShift (#1083)

This commit replaces the service account names for grafana and
prometheus in the instructions to set the security context
constraints for OpenShift.

linsun/istio.github.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,ZackButcher/istio.github.io,istio/istio.io,ZackButcher/istio.github.io,linsun/istio.github.io,linsun/istio.github.io,jasminejaksic/istio.github.io,istio/istio.io,ZackButcher/istio.github.io,geeknoid/istio.github.io,geeknoid/istio.github.io,istio/istio.io,geeknoid/istio.github.io,linsun/istio.github.io,jasminejaksic/istio.github.io,ZackButcher/istio.github.io,geeknoid/istio.github.io,jasminejaksic/istio.github.io,jasminejaksic/istio.github.io,geeknoid/istio.github.io,linsun/istio.github.io