separated spec:unit from spec:unit_quiet

When you run `rake spec:unit`,  bacon stops running tests and shows you the first failure.
This is due to `-q` flag being set by default in our rake task.

It runs in about 1.5 seconds which is quite nice if you're hunting for a particular bug,
so I've kept that behavior as `rake spec:unit_quiet`.
```
29 disabled specifications
524 specifications (0 requirements), 0 failures, 1 errors
rake aborted!
Command failed with status (1): [bundle exec bacon spec/unit/installer_spec...]
/Users/musalj/code/OSS/cocoapods/CocoaPods/Rakefile:172:in `block (2 levels) in <top (required)>'
Tasks: TOP => spec:unit
(See full trace by running task with --trace)
        1.67 real         1.37 user         0.28 sys
```

However, the default `rake spec:unit` task should show all the failures.