Description of problem:

See bug 1835168 and the referenced github issue for general info. Once these are fixed, use this in engine-setup grafana plugin:

1. Put admin password in its own file. Do not overwrite it on updates. Do not ask admin password if the file exists.

2. Put secret_key in its own file. Do not overwrite it on updates if exists.

3. Other stuff? Compare our current grafana.ini template with the one packaged by grafana and decide what should be in its own file.