[HttpKernel][Bundle] Bundle multiple Inheritance

add support of array for Bundle::getParent so bundle could override multiple parents

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes (as Stof note it : returning an array breaks any bundle relying on this method currently)
| Deprecations? | no
| Tests pass?   | yes (same error on 5.3.3 travis build as master repository)
| Fixed tickets | #8071
| License       | MIT
| Doc PR        | -

- [ ] submit changes to the documentation
- [ ] submit changes to the sension/framework-extra-bundle to allow Sensio\Bundle\FrameworkExtraBundle\Templating\TemplateGuesser::guessTemplateName to work with array returned by Bundle::getParent