feat(sys-apps/baselayout): Stop changing the core user's UID

The SDK does not set the `symlink-usr` flag so it has stuck with the old
amd64-generic behavior of setting the core user's UID to 1000. In order
to make running the SDK on CoreOS reasonably sane switch to 500 on both.
Merge pull request #639 from marineam/coreception

feat(sys-apps/baselayout): Stop changing the core user's UID
add(app-emulation/open-vm-tools): Experimental minimal build.

TODO:
 - Move to /usr/share/oem
 - Remove /usr/share/open-vm-tools/messages
 - Remove /etc/vmware-tools (possibly relocate some to /usr/share/oem)

Fixes https://github.com/coreos/coreos-overlay/issues/499