Remove instruction setting ovs_use_veth to True

Remove instruction to set ovs_use_veth to True. Updated kernels shipped
to RDO/RHELOSP, and in RHEL/CentOS 6.5, mean that this is no longer
required. The updated kernels support network namespaces properly.

Change-Id: I6d34f924c1d93b6b7de2b0b7885755e48263a4d4
Closes-Bug: #1268806
backport: havana
(cherry picked from commit e7b8b73550bd71c3702dd11466cbb63cfb752693)
Merge "Remove instruction setting ovs_use_veth to True" into stable/havana