vpnkit-9pmount-vsock: rebase to alpine:3.8
vpnkit-9pmount-vsock: rebase to alpine:3.8

Also remove unnecessary Go toolchain

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit