This patch adds an operation for the NSX-V and two operations for
the NSX-T plugin. The goal of these operation are:
- Find routers without any downlink. They cannot be migrated and
should be removed before migration to NSX-T.
- Patch and restore Neutron routers without gateway. For N/S
cutover, each router must have a T0 uplink or an SR. The 'fixup'
operation ensures the NSX T1 routers for these neutron routers
will have a T0 uplink. (They surely do not have a SR).
The 'restore' operation returns T1 routers to their original state.
Change-Id: Iffd1a5e43e08fdc997a591829c87bcc0bb806c77
f177d2923d