This adds an option, --suppress-outputs, to many commands, to
avoid printing stack outputs for stacks that might contain sensitive
information in their outputs (like key material, and whatnot).
Fixespulumi/pulumi#2028.
This simply refactors all the display logic out of the
pkg/backend/filestate package. This helps to gear us up to better unify
this logic between the filestate and httpstate backends.
Furthermore, this really ought to be in its own non-backend,
CLI-specific package, but I'm taking one step at a time here.
