buildserver: move buildserverid to provisioner

In order to support Docker, this should be able to operate without ssh,
e.g. using vagrant-communicator-docker.  This removes the buildserverid
hack and makes it a provisioner shell script.

buildserver/Vagrantfile

@@ -86,5 +86,7 @@ Vagrant.configure("2") do |config|
   config.vm.provision "shell", path: "provision-android-ndk",
     args: ["/opt/android-sdk/ndk", "r21e", "r22b"]
   config.vm.provision "shell", path: "provision-gradle"
+  config.vm.provision "shell", path: "provision-buildserverid",
+    args: [`git rev-parse HEAD`]
 
 end

buildserver/provision-buildserverid

@@ -0,0 +1,9 @@
+#!/bin/bash -e
+
+test -n "$1"
+
+echo "Writing buildserver ID ...ID is $1"
+set -x
+echo "$1" > /home/vagrant/buildserverid
+# sync data before we halt() the machine, we had an empty buildserverid otherwise
+sync