file: fix close_on_exec for multithreaded decompression

It is not safe to call the 'file' command from multiple threads. When a
file is checked with multiple threads in parallel, the file descriptors
might get shared which makes the pipe handling lock up, leading to lock
up in rpmbuild. And may lead to rarely deadlock on random recipes's
do_package task.

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>