Fixes problems with MR tests

There were a couple problems with the MR integration tests caused
by siblings/tombstones on the non-default bucket type.
This is now corrected by setting allow_mult to false for these
tests.

There is still one MR test that fails and it is legitimate. Using the
4-arity input (bucket, key, keydata, type) with the `default` bucket
type is still broken in Riak. You must use the 3-arity version which
does not specify a type.

Testing these fixes can be done via:

`mvn clean install -Pitest,default -Dcom.basho.riak.buckettype=true -Dcom.basho.riak.2i=true`

With leveldb as the backend and the `test_type` bucket type created and enabled.