Relabel r/w file systems on firstboot path.

The installer currently does all FS relabeling. This seemed like a good idea but it can and has given us problems when doing upgrades over the air (OTA). The "right way" is to relabel all writable file systems on the first boot path. This spreads out the code that does the relabeling a bit but in the end it works in both install & upgrade. I've got another set of changes for the installer that I'll float after we work through this pull request.