Operator can't mark machines as broken without acquiring the machine

[Björn Tillenius]

This is testing with MAAS 2.5.1-7489-g2f25a2cc0-0ubuntu1~18.04.1.

Logged in as a user that has the Operator role in RBAC, I can't mark
a machine in the Ready state as Broken.

I can however mark the machine as broken if I acquire the machine first,
but I see no reason why that should be necessary.

In fact, even a normal user can mark a machine as broken if it's acquired
first, in which case he looses access to the machine and it becomes unusable
for him, with no way of fixing it.

An Operator can mark a Broken machine as fixed.

This bug affects both the UI and the API.