test-container: Always copy test-specific support files [BZ #27537]

There's a small chance that a fresh checkout will result in some of
the test-specific container files will have the same timestamp and
size, which breaks the rsync logic in test-container, resulting in
tests running with the wrong support files.

This patch changes the rsync logic to always copy the test-specific
files, which normally would always be copied anyway.  The rsync logic
for the testroot itself is unchanged.

(cherry picked from commit 20bee713)