Ensure `translator_plugins` config is honored in non-zend-mvc contexts

[weierophinney]

Per https://discourse.zendframework.com/t/validatormanager-not-calling-custom-validator-factory/109/5?u=matthew the translator_plugins config key is not honored currently unless the application is within a zend-mvc context. This is due to the fact that Zend\I18n\Module wires configuration for the Zend\ModuleManager\Listener\ServiceListener in order to push merged service configuration into the plugin during bootstrap; no similar logic is available when not in a zend-mvc context, however.

This patch fixes that situation by modifying the LoaderPluginManagerFactory to do the following:

• If a ServiceListener service exists, it returns the plugin manager immediately (old behavior).
• Otherwise, it checks for the config service, and, if found, a translator_plugins key with an array value. When found, it feeds that value to a Zend\ServiceManager\Config instance and uses that to configure the plugin manager before returning it.

[weierophinney]

Test failures are all on lowest, due to zend-servicemanager test expectation updates to use PHPUnit 5.7/6.0 expectException syntax within the LoaderPluginManagerCompatibilityTest, which is unrelated. When run manually against an earlier zend-servicemanager version, the new tests pass.