[WIP] Add `build.xml` to run testsuite in parallel

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Based of the work that @ocramius has done to speed up the testsuite
running on travis for zf2! https://github.com/zendframework/zf2/pull/3703

On my laptop a full run of the testsuite goes from 1m 36s to 36s. This way we also occupy travis-ci less. :)