Run production suites on Ubuntu Focal.
Added separate success-http-headers files for Focal and Bionic.
Also excluded them from whitespace rules in lint.
memcached 1.5.22 in Ubuntu 20.04 has a bug where it looks for its SASL
configuration at /etc/sasl2/memcached.conf/memcached.conf instead of
/etc/sasl2/memcached.conf.
We already use a workaround for this while applying puppet configurations in
99e71f3786 but for docker builds we used
do memcached hack since we can not use systemd in docker containers.
Anders Kaseorg
arpit551