Add support for setting guestinfo variables

This patch adds an `extra_config` section to the provider configuration which
can be set to a hash. This hash is used to populate the `extraConfig` section
of the `VirtualMachineConfigSpec` used to clone new VMs. The keys of the hash
must start with `guestinfo.` and the values are available to guest VMs with
VMware tools installed via the `vmtoolsd` command.

README.md

@@ -140,6 +140,10 @@ This provider has the following settings, all are required unless noted:
   to the VM upon creation. This method takes a key/value pair,
   e.g. `vsphere.custom_attribute('timestamp', Time.now.to_s)`, and may be called
   multiple times to set different attributes.
+* `extra_config` - _Optional_ A hash of extra configuration values to add to
+  the VM during creation. These are of the form `{'guestinfo.some.variable' => 'somevalue'}`,
+  where the key must start with `guestinfo.`. VMs with VWware Tools installed can
+  retrieve the value of these variables using the `vmtoolsd` command: `vmtoolsd --cmd 'info-get guestinfo.some.variable'`.
 
 ### Cloning from a VM rather than a template
 

lib/vSphere/action/clone.rb

@@ -41,6 +41,7 @@ def call(env)
             add_custom_cpu(spec, config.cpu_count) unless config.cpu_count.nil?
             add_custom_cpu_reservation(spec, config.cpu_reservation) unless config.cpu_reservation.nil?
             add_custom_mem_reservation(spec, config.mem_reservation) unless config.mem_reservation.nil?
+            add_custom_extra_config(spec, config.extra_config)
 
             if !config.clone_from_vm && ds.is_a?(RbVmomi::VIM::StoragePod)
 
@@ -233,6 +234,14 @@ def add_custom_cpu_reservation(spec, cpu_reservation)
         def add_custom_mem_reservation(spec, mem_reservation)
           spec[:config][:memoryAllocation] = RbVmomi::VIM.ResourceAllocationInfo(reservation: mem_reservation)
         end
+
+        def add_custom_extra_config(spec, extra_config = {})
+          return if extra_config.empty?
+
+          # extraConfig must be an array of hashes with `key` and `value`
+          # entries.
+          spec[:config][:extraConfig] = extra_config.map { |k, v| { 'key' => k, 'value' => v } }
+        end
       end
     end
   end

lib/vSphere/config.rb

@@ -26,11 +26,13 @@ class Config < Vagrant.plugin('2', :config)
       attr_accessor :cpu_count
       attr_accessor :cpu_reservation
       attr_accessor :mem_reservation
+      attr_accessor :extra_config
 
       attr_reader :custom_attributes
 
       def initialize
         @custom_attributes = {}
+        @extra_config = {}
       end
 
       def custom_attribute(key, value)