This adds an s390 cross build target to our library of docker setups.
There is an issue with the xfslibs-dev:s390x package having a clash so
we do a || apt-get -f install to fixup the rest of the dependencies.

This doesn't build on the debian.docker file as we are using the
multilib compiler which is only available in stretch (the current
testing repo).
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
CC: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20170227143028.16428-2-alex.bennee@linaro.org>
Reviewed-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>