RHEL: create /etc/openvswitch directory

This directory needs to be created by the package manager
because ovs-ctl is being invoked from SElinux openvswitch
domain that does not have enough privileges to create
directories under /etc on its own.

Without this patch Open vSwitch is not able to start under
SElinux enforcing mode (which is default on CentOS by the way).

Signed-off-by: Ansis Atteka <aatteka@nicira.com>
Ackedy-by: Kyle Mestery <mestery@mestery.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>