openvswitch: Run with nice -10 (#1765)

This is default if ovs is started through ovs-ctl but we start it directly, hence
tell procd to use nice -10 for ovs.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Merge pull request #350 from commodo/ovs-niceness

openvswitch: Run with nice -10 (#1765)