Code review comment for ~redriver/cloud-init:frbsd-azure-branch

There is a lot of good stuff here, thank you for your work and your patience.
Some good things:
 - the generate_fallback_config() is good, thanks.
 - the unit tests added for that and for the resize.

There are some things that still need fixing though, and I have some in-line
comments to help elaborate.
a.) You've fixed some general things inside of the DataSourceAzureNet only.
    Ie, you made devent2deev run through the datasource, which means
    that that code wont work running freebsd on Ec2. Better to have
    logic in it that does the right thing both places.

b.) I think we can simplify the '_can_skip_resize_*' things a bit.:w

c.) is your '_can_skip_resize_ufs' for performance? or is it actually needed?