xenial|bionic-amd64-mbedtls-build: create mbedtls ubuntu dockerfiles

The docker files, and their resulting docker image, are consumed by the
MbedTLS Open CI [1]; the corresponding files were taken
as-it-is from [2], so future changes on these definitions should be
done in this repository instead of [3]

[1] https://linaro.atlassian.net/browse/TFC-4
[2]
https://github.com/ARMmbed/mbedtls-test/blob/master/resources/docker_files/
[3] https://github.com/ARMmbed/mbedtls-test

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: I977bda679cc36f97b0467c938f479ed8ae31810c
4 files changed