package.bbclass: Split into two tasks, one which prepares the packages and then packa...

package.bbclass: Split into two tasks, one which prepares the packages and then package_write which actually generates the packages. The two stage approach allows us to avoid circular dependency issues from classes like debian.bbclass. As the data being emitted into pkgdata/ changed, you need to either wipe tmp or rerun the do_package tasks (wipe the do_package stamps). Everything will repackage anyway due to the new task.