O suporte do Juju para o MAAS 2.0 (que é o que você obterá no Xenial) ainda está em desenvolvimento. O erro que você está vendo parece estar corrigido para o Juju 2.0-beta7:
Tentando inicializar o juju no meu maas, meu não é adquirido depois disso. Não consigo descobrir o que fazer
rama@Maas:~$ juju bootstrap maas maas/172.17.6.253 --to snoutlike-ute.maas --show-log
2016-04-30 17:45:19 INFO juju.cmd supercommand.go:60 running juju [2.0-beta6 gc go1.6.1]
2016-04-30 17:45:19 INFO cmd cmd.go:141 cloud "maas" not found, trying as a provider name
Creating Juju controller "local.maas" on maas/172.17.6.253
2016-04-30 17:45:19 INFO juju.cmd.juju.commands bootstrap.go:482 combined bootstrap constraints:
2016-04-30 17:45:19 INFO juju.network network.go:327 setting prefer-ipv6 to false
Bootstrapping model "admin"
2016-04-30 17:45:19 INFO juju.environs.bootstrap tools.go:90 looking for bootstrap tools: version=2.0-beta6
2016-04-30 17:45:19 INFO juju.environs.tools tools.go:106 finding tools in stream "devel"
2016-04-30 17:45:19 INFO juju.environs.tools tools.go:108 reading tools with major.minor version 2.0
2016-04-30 17:45:19 INFO juju.environs.tools tools.go:116 filtering tools by version: 2.0-beta6
Starting new instance for initial controller
Launching instance
2016-04-30 17:45:20 INFO juju.provider.common destroy.go:22 destroying model "admin"
2016-04-30 17:45:20 INFO juju.provider.common destroy.go:33 destroying instances
2016-04-30 17:45:20 ERROR juju.cmd.juju.commands bootstrap.go:686 error cleaning up: destroying instances: machine 0: blockdevice blockdevice 2.0 schema check failed: model: expected string, got nothing
2016-04-30 17:45:20 ERROR cmd supercommand.go:448 failed to bootstrap model: cannot start bootstrap instance: cannot run instances: cannot run instance: blockdevice 5: blockdevice 2.0 schema check failed: model: expected string, got nothing