Automatically use TLS root certificates from /etc/ssl/certs/

Introduce the optional /config/extratls-certificates.pem for testing and
remove the use of /config/v2tlsbaseroot-certificates.pem

We also remove the v2tlsbaseroot-certificate.pem from the config partition
we build.

Signed-off-by: eriknordmark <erik@zededa.com>

Author: eriknordmark