Add network segment command object in support of routed networks.
This patch set includes documentation, unit tests and functional
tests (currently skipped until segments enabled in neutron by
default) for the following new commands:
- "os network segment list"
- "os network segment show"
These new commands are currently marked as beta commands.
Change-Id: I1a79b48dc6820fe2a39fcceb11c8cae3bda413a0
Partially-Implements: blueprint routed-networks