build-all: stamps directory should be less silly

[geofft]

The build-all infrastructure uses /mit/debathena/machines/$machine/stamps.$suite for the stamps directory. $machine is hard-coded to "awesome-build-server", which is a symlink to debuild. The other directory, mega-man, corresponds to something that has been a SIPB office head and not a build server for about three years. We haven't created a new stamps directory when we moved from debuild to zulu, and haven't ever moved away from the "awesome-build-server" symlink.

This is all silly. We should just use /mit/debathena/stamps or a build-all/stamps or something.

[jdreed]

r25794

I like the ideal of the stamps directory living in build-all, where the Makefile is. However, I dislike build-all living in a sysname-dependent directory. But that's a different ticket.