Remove run-time version checking for openvswitch features

The current method of checking openvswitch and kernel versions for
specific feature support is brittle, distro-specific and unsupportable.

This patch removes the runtime version checks and implements a test
script which allows testing specific neutron features or can test
that all features required by a specific configuration are available.

For example, to test VXLAN support in openvswitch, either:

  neutron-sanity-check --ovs_vxlan

or pass in the deployed configuration files with AGENT/tunnel_types
containing 'vxlan', like:

  neutron-sanity-check --config-file /etc/neutron/plugins/ml2.conf.ini

Deployment tools can then test that the required features exist without
relying on version numbers and without incurring a penalty every time
the agent is started.

Implements: blueprint remove-openvswitch-version-check
DocImpact
Change-Id: I5e822d97b9bece9242ba5ac8901aa0ca4f090cfe
Merge "Remove run-time version checking for openvswitch features"