provider/maas: only bridge specified interfaces

[frobware]

The list of interfaces to be bridged is no longer automatically
determined by the bridge script; you know need to specify a space
separated list of interface names that you want bridging.

For example:

$ add-juju-bridge.py
--interfaces-to-bridge="eth0 eth0:1 eth0:2 bond2" /e/n/i

The MAAS provider now works out which interfaces are to be bridged and
invokes the script with a specific set of interface names. The MAAS
provider will now bridge any interface that has a subnet and is not
unconfigured (i.e., it has an IP address).

Fixes LP:#1627037

[dooferlad]

Pass in MAAS API version and switch.

[frobware]

We should do this as a separate change; there are many other places that pass in / use the result of usingMAAS2().

[dooferlad]

OK, 👍 in that case.

[frobware]

We're going to drop this PR and produce a final-final version.

[frobware]

And... having checked everything we're now going to keep this PR.

[frobware]

I have tested this MAAS 2.0 using a combination of nodes with:

• one nic
• two nics, one unconfigured
• bonded nics, parent unconfigued
• vlan on a bond

And for each scenario I added a LXD container. In one setup I ran into the issue PR #6276 fixes, and indeed it fixed my setup too. For each of these scenarios I visually inspected /etc/network/interfaces on both the host and in the container.

Tested the combinations using xenial.

[frobware]

I have also tested with trusty.

[dimitern]

I tested with trusty on 1.9 MAAS as well, and with xenial (yesterday) on both 2.0 and 1.9 MAAS

[mitechie]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju