Get an abstract defined service from an alias

When you want to get a service leading to to an abstract factory from an alias.

I ended up with this issue when trying to get a cache instance wich i defined in my configuration :

```php
return array(
    'service_manager' => array(
        'abstract_factories' => array(
            'Zend\Cache\Service\StorageCacheAbstractServiceFactory',
        ),
        'aliases' => array (
            'app_cache' => 'memcached',
        ),
    ),
    'caches' => array(
        'memcached' => array(
            'adapter' => array(
                'name' => 'memcached',
                // other config values...
            ),
        ),
    ),
)
```
The purpose is to be able to change the cache by changing the alias.

Without this PR, ZF try to create this service : 
```php
$this->canCreateFromAbstractFactory('memcached', 'cache_core');
```
but 'cache_core' is not a cache configuration key.