Expose novas serial console API for instances

Summary
=======
Nova provides multiple APIs to interact with the console of a launched
instance. These APIs provide connection information for the protocols VNC,
SPICE and RDP. The nova blueprint "serial-ports" [1]_ provides another form of
connection to launched instances. This blueprint wants to implement a console
view in horizon to this serial port.

Motivation
==========
Not every hypervisor platform supports VNC. E.g. the system z (S390) which will
be introduced as a new platform [2]_. To give a user the same look and feel
independent from the underlying hypervisor, a visual representation of the
serial console [1]_ is needed in horizon.

Description
===========
Same usage scenarios as the VNC console tab in instance detail view.

UX
===
The UX should be the same as when a user interacts with the VNC console in
horizons "console" tab of a selected launched instance.

Wireframes, Mocks, Videos and UI Markup
---------------------------------------
It seems that Richard Jones (r1chardj0n3s) used the serial console in his
angboard [3]_ (angularjs OpenStack Dashboard) demo of the kilo summit. His
work is absorbed by this blueprint.

Testing
=======
* Basic workflow:
    * Ensure to have a compute node in your setup which does not support VNC but
       supports serial console.
    * Launch instance on this node
    * Open console tab in horizon of this instance
* Launch in full-screen console
* Validate failover from VNC, etc. to SERIAL. as well as ``CONSOLE_TYPE=SERIAL``

Outside Dependencies
====================
* Term.js
* The nova client implements this with "nova get-serial-console" [4]_.
* The nova v2.1 (formerly v3) api implements this with the server action
``os-getSerialConsole`` [5]_.

Requirements Update Required
============================
N/A

Doc Impact
==========
N/A

References
===========
.. [1] https://blueprints.launchpad.net/nova/+spec/serial-ports
.. [2] https://blueprints.launchpad.net/nova/+spec/libvirt-kvm-systemz
.. [3] https://github.com/r1chardj0n3s/angboard/search?utf8=%E2%9C%93&q=console
.. [4] http://docs.openstack.org/cli-reference/content/novaclient_commands.html#novaclient_subcommand_get-serial-console
.. [5] https://github.com/openstack/nova/blob/master/doc/v3/api_samples/os-remote-consoles/get-serial-console-post-req.json