docker: Fix travis.py parser and misc change

docker: Fix travis.py parser and misc change

Fixed the travis.py script that has failed to parse the current
QEMU_SRC/.travis.yml file. It no longer makes combinations from
env/matrix, instead it uses explicit includes. Also the compiler
can be omitted from matrix/include, so that Travis chooses the
first entry of the global compiler list.

Replaced yaml.load() with yaml.safe_load() so that quieting the
following deprecation warning:
https://github.com/yaml/pyyaml/wiki/PyYAML-yaml.load(input)-Deprecation

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-Id: <20190320221207.11366-2-wainersm@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>