debian, rhel, xenserver: Ability to collect ovs-ctl logs.

debian, rhel, xenserver: Ability to collect ovs-ctl logs.

We use ovs-ctl from startup scripts to start, stop, restart,
force-reload-kmod OVS daemons. ovs-ctl gives quite a descriptive
o/p while running the above commands. But the o/p goes to stdout.
Sometimes, this output is quite useful to debug issues.

With this patch, we store the o/p of ovs-ctl when called from
startup scripts in /var/log/openvswitch/ovs-ctl.log

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>