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. 

I ended up working (read: hacking) around this 
in the top-level user API that generates a query
by using the 3-arity when the type is `default`
but left the core test that manually constructs the 
JSON for a MR query there to show this is indeed broken. 

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.