Comment 1 for bug 1361374

In the mid- to long-term juju will be more flexible in the networking setup and allow static IPs and bridges to be configured as needed (not only for MAAS), but this will come along as we implement more of the networking model.

In the short-term, I propose to implement a "safety switch" environment setting (a flag, false by default) "disable-network-management", which when set will prevent juju from trying to configure or manage networking on the machines AT ALL (i.e. the networker will run in safe mode and the maas provider in particular won't change the networking setup during cloudinit). This should fix your immediate issue.

Off-topic: There seems to be some misunderstanding, as as far as I know it was decided to allow juju to manage the networking in a maas environment (at least for this cycle). If both Juju and MAAS try to manage networking there are bound to be issues and we need to work together more closely.