DDC-2389: [GH-642] replaced direct class in instance creation

[doctrinebot]

Jira issue originally created by user @beberlei:

This issue is created automatically through a Github pull request on behalf of dmishh:

Url: #642

Message:

return new EntityManager() -> return new static() on line 945
made code more reusable

[doctrinebot]

Comment created by @beberlei:

A related Github Pull-Request [GH-642] was closed
#642

[doctrinebot]

Comment created by @Ocramius:

EntityManager should not be extended

[doctrinebot]

Issue was closed with resolution "Invalid"

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-642] was closed:
doctrine/dbal#642