When https_proxy is set, use proxy opener to open CVE metadata and
database URLs, otherwise fallback to the urllib.request.urlopen.
Also fix a minor issue where the json database which has been gzip
decompressed as byte object should be decoded as utf-8 string as
expected by update_db.
Signed-off-by: Chin Huat Ang <chin.huat.ang@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
