On v2019 `libtool` now detects it doesn't need the fast-install mode and thus
leaves `relink_command` empty in the executable wrappers it generates.

Unfortunately, to avoid conflicts with the system AppArmor profile, the
tests using `canterbury-update-component-index` relied on the wrapper
triggering a relink and thus re-generating the binaries in the right place
when moved around.

Since `relink_command` is now empty this no longer happens and the tests fail
as they can't find the real executable to launch:

    $ ./component-index.t
    /component-index/get-bundle: /tmp/canterbury.N9IZ0Z/canterbury-update-component-index: error: '/tmp/canterbury.N9IZ0Z/.libs/canterbury-update-component-index' does not exist
    This script is just a wrapper for canterbury-update-component-index.
    See the libtool documentation for more information.
    **
    Canterbury:ERROR:tests/common.c:132:tests_temp_component_index_update: assertion failed (error == NULL): Child process exited with code 1 (g-spawn-exit-error-quark, 1)

Rather than relying on this implict behaviour, let's also copy the `.libs`
folder containing the real built binaries.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>