Added mongodb_standalone recipe

I've changed the recipe name from mongodb::10gen_repo to mongodb_org_repo because https://github.com/edelight/chef-mongodb/blob/master/recipes/10gen_repo.rb#L1 .

I've changed tests from bats to serverspecs

I've added 2 suites (one for testing mongodb as it (runlist_mongodb_standalone) and one to run it from a wrapper (wrapper_mongodb_standalone)) rather than having a big run list with everything. It think it's making things easier to test locally, and force us to have modular recipe not depending on each other. 

I was looking for details about the wrapper suites kitchen process, it might be nice to talk about it further as we started to use it in stack-commons and phpstackt but I'm not sure to understand how it's supposed to work once implemented.