Fix single run of encryption tests and usages of uniqid() and fopen()

apps/files_encryption/lib/stream.php

apps/files_encryption/tests/crypt.php

apps/files_encryption/tests/helper.php

apps/files_encryption/tests/hooks.php

apps/files_encryption/tests/keymanager.php

apps/files_encryption/tests/proxy.php

apps/files_encryption/tests/share.php

apps/files_encryption/tests/stream.php

apps/files_encryption/tests/testcase.php

apps/files_encryption/tests/trashbin.php

apps/files_encryption/tests/util.php

apps/files_encryption/tests/webdav.php