The connection cache class uses a dummy file object but it doesn't have a closed
attribute, so we can't use it in a context manager.
(Bitbake rev: 7b072ef91d16331eae11bd60f229ce1f0c175995)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>