LDAP: create a new instance of Configuration on clone, fixes #7803

Upon login a bind is done with the user credentials which is valid for the whole LDAP resource. It needs to be reset to the agent's credentials. So on the authentication check, the Connection instance is cloned, but the underlying Configuration is a class of it's own since OC 6. I.e. when cloning a new instance of it needs to be created. 

Unit test included.

Please test and review @uka-support @Xenopathic or others