#130 Add support to spork to rails.new tests

Start spork server with
`./tools/bin/go.jruby -S rake --rakefile server/run_rspec_tests_use_new_rails.rake spork`

And run tests with
`./tools/bin/go.jruby -S rake --rakefile server/run_rspec_tests_use_new_rails.rake spec`

The default rake task for running specs uses `--drb` to connect to spork. This shouldn't be a problem cince it will fallback to local run if spork server is not running.

At the moment, the test runner exits with a non-success code like in this example:

```
.

Finished in 0.297 seconds
1 example, 0 failures

Randomized with seed 22868

  <-- Slave(1) run done!
TypeError: can't convert DRb::DRbObject into Integer
    exit at org/jruby/RubyKernel.java:879
    exit at org/jruby/RubyKernel.java:860
  (root) at /Users/rjunior/code/github/gocd/server/../tools/bin/go.rspec:26
rake aborted!
```
This happens due a bug in spork (reported in sporkrb/spork#240).