Using `time` to calculate the average of 100 iterations on my machine,
`packer` went from 130ms on average to 70ms.

Previously, the load time would scale linearly about 30ms (on my
machine) on average per new command added. Now that is much much
smaller.

This command prints out the components of a template, and most
importantly respects the machine-readable flag so that you can
programmatically inspect a template's contents without manually parsing
the JSON.

/cc @markpeek

This just kind of shields the error with StartWithUi if we retry

builder/amazon/common: added passing UserData to goamz.