Add support to ppc64le builds in Travis. This duplicates the number of
jobs that runs from Travis. All jobs from the matrix are supported in
ppc64le.

Support for ppc64le builds runs only on Xenial & Bionic and only from
inside a LXD container[1]. There is a limitation in running Docker
from inside LXD, the ones relevant for us are: '--privileged' and
'-t'. I am not sure we really need the later and the former is only
needed to create a tmpfs /tmp. The tmpfs can be done from outside
docker and just exported to it with a bind-mount or directly using the
specific '--tmpfs' docker-run option. I choose the later. For the
output/tty redirection (-t), docker on travis + ppc64le runs inside an
LXD container and for security limits what can be done inside it, and
as such, `docker run` fails with "the input device is not a TTY" when
using -t because of limited permissions to /dev imposed by LXD, so for
now I am disabling it for ppc64le builds (it is already disabled for
GHA), and if it is not really needed we can remove it all together.

Some parts of docker image build and package generation had x86_84
hardcoded and needed to be fixed.

[1] https://docs.travis-ci.com/user/reference/overview/


    #virtualisation-environment-vs-operating-system

Signed-off-by: Raoni Fassina Firmino <raoni@linux.ibm.com>