add unit test to have one default repository

git-svn-id: http://svn.redmine.org/redmine/trunk@12492 e93f8b46-1217-0410-a6f0-8f06a7374b81
Rails4: replace deprecated Relation#update_all at Repository model

git-svn-id: http://svn.redmine.org/redmine/trunk@12493 e93f8b46-1217-0410-a6f0-8f06a7374b81
Rails4: replace deprecated Relation#update_all at SetDefaultRepositories db migration

git-svn-id: http://svn.redmine.org/redmine/trunk@12494 e93f8b46-1217-0410-a6f0-8f06a7374b81