On clone create a new instance of the Configuration

To avide effects on the original instance of Connection when the clone
is modified, for instance on authentication checks.
Use array_key_exists instead of isset, because the latter returns false if the assigned value is null
add test for cloning and keeping configuration seperate
Merge pull request #7844 from owncloud/fix_7803_blizzz

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