containerboot's main.go had grown to well over 1000 lines with
lots of disparate bits of functionality. This commit is pure copy-
paste to group related functionality outside of the main function
into its own set of files. Everything is still in the main package
to keep the diff incremental and reviewable.
Updates #cleanup
Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>
