utils: create_cmdline_shebang_wrapper preserve permission and ownership

The .real command was not given the same permissions and ownership as
the original pre-wrap file and this is now fixed.

A situation where the original pre-wrap file did not have write
permissions would cause a failure in the wrapping is also fixed.

Test update also included.

Signed-off-by: Paulo Neves <ptsneves@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>