[WIP] Multiple environments and centralization



This PR:

1. Removes the duplication in the test bootstrapping for the various bundles by adding a single generic configuration in TestBundle as a base.
2. Allows the entire test suite to be run with any combination of `postgres|mysql`, `jackalope-jackrabbit| jackalope-doctrine-dbal`.

The environment can be defined with:

- `SULU_PHPCR`: Name of PHPCR implementation, either `jackrabbit` or `doctrine_dbal`
- `SULU_ORM`: Name of database implementation to use, either `mysql` or `postgres`.

Tests can be executed as follows:

````
$env SULU_ORM=mysql SULU_PHPCR=jackrabbit ./bin/runtests.sh --t SearchBundle
````

__Tasks:__

- [ ] Finish porting the tests


__Informations:__

| Q             | A
| ------------- | ---
| Fixed tickets |  [#479]
Setting the context to ADMIN works for all the existing tests. I don't know if we will need to make this mutable in the future.