tools/xenstore: handle CLOEXEC flag for local files and pipes

tools/xenstore: handle CLOEXEC flag for local files and pipes

For support of live update the locally used files need to have the
"close on exec" flag set. Fortunately the used Xen libraries are
already doing this, so only the logging and tdb related files and
pipes are affected. openlog() has the close on exec attribute, too.

In order to be able to keep the event channels open specify the
XENEVTCHN_NO_CLOEXEC flag when calling xenevtchn_open().

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Julien Grall <julien.grall@amazon.com>
Acked-by: Wei Liu <wl@xen.org>