Add "router list" command. It takes one "--long" option.
By default, the command will print router id, name, status,
admin state up, distributed, ha and project id.
With "--long" option, it will also print routes and
external gateway info.
Change-Id: I9d21904c41c11ee1fa107f985744878a1dc2f970
Implements: blueprint neutron-client
Partial-bug: #1519503
