Merge pull request #13490 from owncloud/fix_reshare_s2s_share

apps/files_sharing/ajax/external.php

apps/files_sharing/api/server2server.php

apps/files_sharing/application.php

apps/files_sharing/lib/controllers/sharecontroller.php

apps/files_sharing/lib/external/manager.php

apps/files_sharing/lib/hooks.php

apps/files_sharing/tests/server2server.php

lib/private/security/certificatemanager.php

lib/private/server.php

tests/lib/security/certificatemanager.php