'router-gateway-set' does not support external gateway ip

[shihanzhang]

now the ' router-gateway-set' does not support external gateway ip,
root@controller:/opt# neutron help router-gateway-set
usage: neutron router-gateway-set [-h] [--request-format {json,xml}]
                                  [--disable-snat]
                                  router-id external-network-id

Set the external network gateway for a router.

positional arguments:
  router-id ID of the router.
  external-network-id ID of the external network for the gateway.

optional arguments:
  -h, --help show this help message and exit
  --request-format {json,xml}
                        The XML or JSON request format.
  --disable-snat Disable source NAT on the router gateway.

we can add a parameter to support it, like:
usage: neutron router-gateway-set [-h] [--request-format {json,xml}]
                                  [--disable-snat][--fixed-ip]
                                  router-id external-network-id

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/163332

[Haifeng.Yan (yanheven)]

a bp have been merged https://review.openstack.org/#/c/181682/

[OpenStack Infra (hudson-openstack)]

Change abandoned by Kyle Mestery (<email address hidden>) on branch: master
Review: https://review.openstack.org/163332
Reason: This review is > 4 weeks without comment, and failed Jenkins the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.