Comment 1 for bug 1733354

It seems for some credentials, or possibly just in some regions, m3.medium is no longer available.
I believe for 'juju bootstrap' we actually switched to t2.medium because of cpu vs cost issues.
I believe a lot of AWS has transitioned to M4.
But ultimately, we seem to be hard coding an instance type that used to be very common, but isn't guaranteed to be available, which means we don't fall back to a different type based on CPU/Mem/etc.
We should rethink how we do instance type selection, and possibly roll out changes to several different Juju versions.

Interestingly, it seems when using EC2 Classic m3.mediums *are* available.