This adds a new driver for Cumulus switches that support using NCLU.
It actually uses the netmiko linux driver, given we are really just
accessing a debian user space, and there is currently no cumulus
specific driver in netmiko.

It borrows quite heavily from the support in networking-ansible that
uses these roles to configure cumulus switches:
https://github.com/ansible-network/network-runner

However, this driver adopts the more typical networking-generic-switch
configuration operations, where existing port configuration is retained
as the port cycles through various VLANs. In a similar way, we make
disabling a port optional, and support users specifying a default VLAN,
such as the ironic inspection network.

Change-Id: I4d96ea3f3c3d55ff7d742b9e08aa75ce990eee9a

When you have around 60 baremetal nodes attached to a single switch, it
takes a long time to execute all those commands. This gets worse when
you limit the number of concurrent ssh connections.

Here we look to batch up commands to send to the switch together, then
wait for them all to complete before returning the result. It does this
by using etcd keys as a queueing system. We pull off the queue using the
version at which the keys were added, giving a FIFO style queue.

Change-Id: I8c458bbc94df5630cfede5434bcdbe527988059c

Change-Id: If2eeb49202b83d59197f1577982b05db1534b894

Change-Id: I3e527f08d3f939a929fd06412d4e0e843891510d

Change-Id: Ie1eef0337775ec4ad04ce0e83352b75fd987a12c