Ok, i finally found a way to login, using username "admin" and password that I
have created when installing hosted engine.
I thought the Grafana login was connected to Keycloak or the oVirt internal SSO database,
but as far as I can see, Grafana account is created during the installation of
Hosted-engine, and subsequent password changes in Keycloak or the internal SSO database do
not affect the Grafana login credidentials, you have to use ones you have created during
installation.