recipes: Replace "cp -a" with "cp -R --no-dereference --preserve=mode,links"

* Using "cp -a" leaks UID of user running the builds, causing
  many QA warnings.
* See this thread for details:
  http://lists.openembedded.org/pipermail/openembedded-core/2015-November/112904.html



Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>