tests: Fix `make check` on v2019

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.