Add network segment range command object in support of network segment
range management.

This patch set includes documentation, unit tests and functional tests
(currently skipped unit network segment range enabled in Neutron by
default) for the following new commands:
  - "os network segment range create"
  - "os network segment range delete"
  - "os network segment range list"
  - "os network segment range set"
  - "os network segment range show"

Co-authored-by: Allain Legacy <Allain.legacy@windriver.com>

[depends on removed by dtroyer as those are all +W and 
trying to pass the gate, OSC has it's freeze dealine looming]
 Depends: https://review.openstack.org/624708
 Depends: https://review.openstack.org/624709
 Depends: https://review.openstack.org/638386

Partially-implements: blueprint network-segment-range-management
Change-Id: I335692f2db5be07c1c164f09b13f1abb80b7ba33

This patch explicitly points out the change needed while
forming the detailed lists for servers. In those cases
where the server response for ``openstack server list``
has the flavor and image keys missing for the instances
in the down cell, the servers will be skipped from being
processed.

Depends-On: https://review.openstack.org/591657/
Related to blueprint handling-down-cell
Change-Id: Ibcfe9febdc45db1cb86c6e88f65976feceb01c02

since nova api 2.40 the os-simple-tenant-usage API supports pagination
and will by default return a number of entities configured internally in
Nova.
This means that when there are many enough projects,
the single call to usage.list() will not return usages for all projects.

This patch effectively copy-pastes the logic to paginate over usage list
results from novaclient/v2/shell.py code.

Change-Id: I1b639fe386b7b7db3223f6965495094b9d51533a
Story: #2005099
Task: #29713