Add spec for Persistence module
user
```ruby
require 'spec_helper'

describe "DatastaxRails::Base" do
  describe "persistence" do
    describe "#create" do
      it "should persist at the given consistency level" do
        DatastaxRails::Base.connection.stub(:execute_cql_query)
        DatastaxRails::Base.connection.should_receive(:execute_cql_query).with(/USING CONSISTENCY LOCAL_QUORUM/i).and_return(true)
        Person.create({:name => 'Steven'},{:consistency => 'LOCAL_QUORUM'})
      end
    end
    
    describe "#save" do
      it "should persist at the given consistency level" do
        DatastaxRails::Base.connection.stub(:execute_cql_query)
        DatastaxRails::Base.connection.should_receive(:execute_cql_query).with(/USING CONSISTENCY LOCAL_QUORUM/i).and_return(true)
        p=Person.new(:name => 'Steven')
        p.save(:consistency => 'LOCAL_QUORUM')
      end
    end
  end
end
```
assistant