Pin docker version in vagrant VM

Otherwise it will always install the latest docker version, which will be
undesirable when new major releases are done, until they are well tested.

For instance, docker after automatically updating to 1.9, it was killing my VM
when spawning a kubernetes cluster, due to a high CPU consumption, probably due
to https://github.com/docker/docker/issues/17720

Vagrantfile

@@ -5,7 +5,7 @@ require './vagrant-common.rb'
 vm_ip = "172.16.0.3" # arbitrary private IP
 
 pkgs = %w(
-  docker-engine
+  docker-engine=1.10.2-0~wily
   aufs-tools
   build-essential
   ethtool