Include build info in output package's metadata

[cuzelac]

We should be able to query a .rpm or .deb package's metadata to determine info about how it was built.

I'm thinking at least:

• system info (uname -a output)
• cmdline and args run to build the package
• build system fqdn
• user
• revision control system specific information
  • p4 counter/git sha/svn-whatever at the time of build
  • branches/tags/etc that were specific to the build
• What else?

The goal is to make it simple to reproduce the package build given only the output package.