Azure / GitLab / Travis: Add Kconfig unit tests to a job

The Kconfig language provides a unit test that can be run.  As these
require pytest to be installed and run very quickly, bundle them in to
an existing CI job.

Signed-off-by: Tom Rini <trini@konsulko.com>
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Changes in v2:
- Have Azure use O=${UBOOT_TRAVIS_BUILD_DIR} as pwd is not writable.