Add linux-run-hooks command for use by package maintainer scripts

Add a linux-run-hooks command as a fairly simple wrapper around run-parts. This is intended to be used by maintainer scripts instead of directly calling run-parts. The benefits of that are:

• It supports use of multiple hooks directories (under /etc/kernel and /usr/share/kernel) if debianutils is new enough, but still works with older versions if only one hooks directory is present.

• The arguments to hooks are documented and the number of arguments is validated.

• The same logic can be shared with Ubuntu and any other derivatives that have their own packaging.