tests/docker: test-build script

Much like test-quick but only builds. This is useful for some of the
build targets like ThreadSanitizer that don't yet pass "make check".

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

Message-Id: <20161011161625.9070-3-alex.bennee@linaro.org>
Signed-off-by: Fam Zheng <famz@redhat.com>
