tools: hv: Use CLOEXEC when opening kvp_pool files

Use CLOEXEC flag when opening kvp_pool_x files to prevent file
descriptor leakage. Not using it was causing a problem when
SELinux was enabled.

Signed-off-by: Tomas Hozza <thozza@redhat.com>
Acked-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>