According to info in https://bugs.launchpad.net/tripleo/+bug/1640812
when setting a OVS bridge with physical interface we need to
define fail_mode in OVS_EXTRA parameter of ifcfg to make
sure it's set at the desired mode after reboot.
This patch adds new parameter fail_mode to vs_port (as ifcfg is created
as part of vs_port, not vs_bridge) and defaults it to required value "standalone".
Similar patch was implemented to os-net-config in
e479535b50
Change-Id: I5f7448e3504c9190d7fe5f4a7958c604ef91a058
Closes-Bug: #1656795
026f64ade4