LXD support (maybe)

[Ian Booth]

> 
>> I personally encourage us to use heterogeneous versions of go as much as
>> we can. Because we should be compatible as much as possible. But it does
>> look like our dependencies are going to force our hand.
>>
> 
> Agreed. I think it's healthy for Juju's devs to be using a range of Go
> versions (within reason). It helps to ensure we not relying on version
> specific behaviour.
> 

+1. And I like life on the edge, so 1.6 for me :-D