Kube baymodel create should allow no network_driver specified

[Dane LeBlanc]

When a kubernetes baymodel is created, the current API validation
only allows an explicit setting of "flannel" for the network_driver
attribute. This validation needs to be changed to allow a user to
create a kubernetes baymodel without explicitly specifying a
network_driver. When no network_driver is explicitly selected,
Magnum should choose the default network driver for the selected
COE type, i.e.:
- Kubernetes: default network driver = flannel
- Swarm: default network driver = legacy docker networking (for now,
               may change to flannel or libnetwork in the future)
- Mesos: default network driver = legacy docker networking

A secondary issue is that for creation of swarm and mesos baymodel
types, no API validation is currently being done for network_driver
(e.g. user is allowed to specify "flannel", but this network driver
is not supported yet for swarm and mesos).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/230147

[Egor Guz (eghobo)]

@leblancd: I think Tom is already committed the patch

[Dane LeBlanc (leblancd)]

@Egor: Thanks, I changed the bug title and description to account for
the other commit: https://review.openstack.org/#/c/228838/.
The new bug(s) being described here are:
- For kubernetes baymodel create, user should be able to
  leave out selection of network-driver altogether
  (magnum should in this case default to flannel).
- For swarm and mesos baymodel create, there is
  currently no network-driver validation being performed
  at all (e.g. "flannel" network-driver is allowed, even
  though flannel isn't currently supported for swarm/mesos
  bays).

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/230147
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=fd2e76054153f77f21d987860adc20e4a0944865
Submitter: Jenkins
Branch: master

commit fd2e76054153f77f21d987860adc20e4a0944865
Author: Dane LeBlanc <email address hidden>
Date: Thu Oct 1 16:44:45 2015 -0400

    Baymodel create should allow no network_driver specified

    When a kubernetes baymodel is created, the current API validation
    only allows an explicit setting of "flannel" for the network-driver
    attribute. This validation needs to be changed to allow a user to
    create a kubernetes baymodel without explicitly specifying a
    network driver. (The same goes for docker swarm and mesos baymodels,
    that is, baymodel create should allow the user not to specify
    a network-driver, but this is the current behavior).

    When no network-driver is selected for baymodel create for a
    given COE, Magnum should choose the default network driver for that
    COE. Note that this change set only handles the validation for
    the case where no network-driver is selected; mapping this to
    the COE-dependent default network driver will be done in other
    commits (e.g. https://review.openstack.org/#/c/224367/ for swarm).

    Note that no new unit test cases were added for this patch since
    test_create_baymodel_with_network_driver and
    test_create_baymodel_with_no_network_driver test cases in
    test_baymodel.py should cover this change.

    Change-Id: I0735f79354bc9fdb141e7a559517268e8ab648ec
    Closes-Bug: 1501077