tests/docker: better handle symlinked libs

tests/docker: better handle symlinked libs

When we are copying we want to ensure we grab the first
resolution (the found in path section). However even that binary might
be a symlink so lets make sure we chase the symlinks to copy the right
binary to where it can be found.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Robert Foley <robert.foley@linaro.org>
Message-Id: <20200203090932.19147-3-alex.bennee@linaro.org>