Disconnected specs

Another step in specs cleanup. 

- I noticed on the plane that without network connection, the rspec runner was simply exiting and not executing the tests and not reporting errors. The problem was related to launching the rspec runner in a thread, this is now fixed. While at it I cleaned a little bit runner.rb for the specs handling. Now, the root crash cause when there's not network connection occurs in `filters/dns` which I did not fix yet, but at least, it is crashing and reporting the error :P

- I also noticed that `make test` was not including test files in the root of `spec/` - which made me discover a remaining spec file utf-8 encoding issue. To run all specs manually you should use `bin/logstash rspec spec/{*.rb,**/*.rb}`

- I noticed `spec/speed.rb` was doing performance tests so I tagged it and noticed the use of `ENV["SPEEDTEST"]` in some specs, so I replaced that for the `:perfomance` tag

- I fixed some performance tests and also made the output more consistent. 

I think that's about it.