app-emulation/open-vm-tools: Add open-vm-tools

Stripped down open-vm-tools ebuild for installing to /usr/share/oem

Based on efforts by:
    Camilo Aguilar <camilo.aguilar@gmail.com>
    Alex Crawford <alex.crawford@coreos.com>
board-packages: build open-vm-tools binary packages.
oem-vmware: Add VMware OEM package, uses open-vm-tools

Originally contributed by Camilo Aguilar <camilo.aguilar@gmail.com>