Hello,
I had exactly the same problem.
I Started the grafana service before setting it up with engine-setup on a Hosted Engine.
and was unable to get to the login page.
I followed the proposed workaround : stopped grafana, removed /var/lib/grafana/grafana.db
and ran engine-setup --reconfigure-optional-components again
I can no log into grafana with admin user, but there is no pre installed dashboard or
data sources available.