elm_config: replace ecore_file_cp with ecore_file_mv

ecore_file_cp can cause config data(eet file) invalid,
once multiple processes are trying to call elm_config_save.

this patch replaces it with ecore_file_mv to prevent the problem.

Reviewed-by: Cedric BAIL <cedric.bail@free.fr>
Differential Revision: https://phab.enlightenment.org/D10578