add (some) registration tests

Change-Id: I70a399751c51ce424481476e45c5c6411d9fada8
calculate the tenants to be registered programmatically

The tenants are now derived from the users hash. Previously the tenants
list had to be provided independently which could cause user errors.

This should also make it easier for wrapper cookbooks which don't have
to calculate the tenants themselves from the users list.

Change-Id: If3ad9840f5b224fa2938a6288df929385335ea38