Make the adminuser independent from LDAP and Github

SF needs an admin user during deployment to create the config repository (for
example). However, currently this is only possible with a configured LDAP
backend or the built-in dummy LDAP, that is only available on domain tests.dom.

This patches modifies the authentication and allows to configure another
admin user that is independent from all other authentication sources.

The admin password is stored hashed and salted on the managesf node.

Change-Id: I8c71b2f84f201cae3959017916d2f54180499aed
Merge "Make the adminuser independent from LDAP and Github"