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.
Since we use this option in our docker-zulip project also
so rather than using it as a test suite option we made it
more specific i.e. --build-release-tarball-only.
arpit551
Aman Agrawal