Merge pull request #5032 from owncloud/fixing-5006-master

Test OC_User_Database in Test_User_Database instead of OC_User_Dummy.

* owncloud/fixing-5006-master:
  Use strict comparison === instead of ==.
  Adjust return value tests for checkPassword() to what OC_User_Example says.
  Make OC_User_Dummy::checkPassword() compatible with OC_User_Example.
  Use parent:: in Test_User_Database::getUser().
  Test_User_Backend::getUser() does not return an array, it returns a string.
  Test OC_User_Database in Test_User_Database instead of OC_User_Dummy.