Fix grafana install rpm key
Fix grafana install rpm key

Grafana install failed on importing the rpm key when using -c local
because the local user was a nonroot user. Other tasks are properly
marked with become: true, so I just added it here

Change-Id: Ia354647b69dc4409795bb6c4fb7afec498a708c4

jkilpatr/browbeat,jkilpatr/browbeat