Update a few build tags to be more generic, add a couple more SETNS constants, and update Travis with a bunch of fixes/tweaks (including removing the nonfunctional cross-compile stuff for now)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #104 from tianon/more-generics

Update a few build tags to be more generic, ...