Refactor LBHttpSolrClient to consolidate the two different request implementations

LBHttpSolrClient has two duplicate request implementations:

1. public Rsp request(Req req) throws SolrServerException, IOException
2. public NamedList<Object> request(final SolrRequest request) throws SolrServerException, IOException

Refactor the client to provide a single implementation that both can use since they should be consistent and are non-trivial implementations which makes maintenance a bit more burdensome.