Moving/Migrating from magma <10% RR to couchstore should be prohibited.

We are adding a new feature Couchstore to Magma upgrade. However ns_serv team also wants to support Magma to Couchstore upgrade. I guess this is a special scenario we need to prevent upgrade to couchstore since magma supports 1% dgm and couchstore 10%. An edge case, but might be worthwhile checking.

Apart from this so far we always had homogeneous buckets either magma or couchstore. Since we can have mixed mode buckets going forward, we need to test that as well.

cc: Balakumaran Gopal