add_tenants logic:
a) allow add tenant only if flavor already assigned to region(s)
b) each tenant in the request will be validated against the
regions assigned to flavor - at least ONE tenant must
pass validation:
i. if NO tenant in tenant list is associated with any of the
regions assigned to the flavor, Ranger will reject the
request entirely and user will be prompted to submit new
request with valid tenants.
ii. only the tenants in tenant list that pass validation will
be kept in flavor tenant list; those that failed
validation will be DROPPED from the tenant list.
delete_region logic (only for flavors with tenants):
a) if a tenant is associated only with the deleted region, the
delete_region logic will delete the tenant from fms table
and the tenant is dropped from the tenant list.
However, if the tenant is associated with other regions still
assigned to the flavor, the tenant stays in the list.
Change-Id: I31935477733c8597741cf7c7c57350ab1e2b4452
385b4b7723