python3: ignore CVE-2015-20107

python3: ignore CVE-2015-20107

CVE-2015-20107 describes an arbitrary command execution in the mailcap
module, but this is by design in mailcap and needs to be worked around
by the calling application.

Upstream Python will be documenting this flaw in the library reference,
and it is likely that the mailcap module will be deprecated and removed
in the future.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>