Small changes to FreeBSD 10 build process

* `:sudo_cmd` changed to actually use `sudo` instead of `su`. The latter really only works as long as the `root` user's password is empty.

* Installs `pkg` early in the process so that `bash-static` and `sudo` can be part of the system early on. Allows for `bash` to be set as the `vagrant` user's shell and also allows for `postinstall.sh` to be a `sh` script instead of (horror) `csh`

* Tweaked install of `ca_root_nss` to set `WITH='ETCSYMLINK'` on the command line so it doesn't have to be in `make.conf`