profiles: fix some ebuilds that depend on CROS_SDK_HOST being set

At some point this variable stopped getting set properly in SDK ebuild
environments. It is currently used to filter out some build time files
from target images. Could be done cleaner but that can come later.
coreos-base/coreos: add xfs-progs to base image

Was requested *AGES* ago but kept forgetting to actually do it. :(
Merge pull request #997 from marineam/xfs

Add xfs-progs, fix e2fsprogs build