Improve the speed of finding an individual VM

This PR makes use of the
[ContainerView](https://www.vmware.com/support/developer/vc-sdk/visdk41pubs/ApiReference/vim.view.ViewManager.html)
to retrieve a cut down list of servers from which the desired object can
be found, after which the object itself can be downloaded. Previously,
we'd download each VM (about 3.5K and several round trips to the server)
to find the VM we want.

From
```
sean~/play/knife-vsphere (find_speed %)$ time knife vsphere vm disk list myserver
  0          Hard disk 1      nosnapshots_ds4 64.00 GiB

real    1m56.153s
user    0m9.536s
sys    0m1.713s
```
to
```
sean~/play/knife-vsphere (find_speed *%)$ time be knife vsphere vm disk list myserver
/Users/sean/.gem/ruby/2.4.1/gems/builder-3.2.2/lib/builder/xchar.rb:111: warning: constant ::Fixnum is deprecated
  0          Hard disk 1      nosnapshots_ds4 64.00 GiB

real    0m2.929s
user    0m1.038s
sys    0m0.236s
```

This'll have to be retrofitted to the other commands, which we can do
over time.

See vmware-archive/rbvmomi#117 for some more context

lib/chef/knife/search_helper.rb

@@ -0,0 +1,41 @@
+# Some helpers for faster searching of the inventory
+module SearchHelper
+  # Retrieves all the VM objects and returns their ObjectContents
+  # Note that since it's a ObjectContent coming back, the individual
+  # object's [] will return only the properties you asked for
+  # and `#obj` will return the actual object (but make a call to the server)
+  # param [Array<String>] properties to retrieve
+  # @return [Array<RbVmomi::VIM::ObjectContent>]
+  def get_all_vm_objects(properties = ['name'])
+    pc = vim_connection.serviceInstance.content.propertyCollector
+    viewmgr = vim_connection.serviceInstance.content.viewManager
+    root_folder = vim_connection.serviceInstance.content.rootFolder
+    vmview = viewmgr.CreateContainerView(container: root_folder,
+                                         type: ['VirtualMachine'],
+                                         recursive: true)
+
+    filter_spec = RbVmomi::VIM.PropertyFilterSpec(
+      objectSet: [
+        obj: vmview,
+        skip: true,
+        selectSet: [
+          RbVmomi::VIM.TraversalSpec(
+            name: 'traverseEntities',
+            type: 'ContainerView',
+            path: 'view',
+            skip: false
+          )
+        ]
+      ],
+      propSet: [
+        { type: 'VirtualMachine', pathSet: properties }
+      ]
+    )
+    pc.RetrieveProperties(specSet: [filter_spec])
+  end
+
+  def get_vm_by_name(vmname)
+    vm = get_all_vm_objects.detect { |r| r['name'] == vmname }
+    vm ? vm.obj : nil
+  end
+end

lib/chef/knife/vsphere_vm_disk_list.rb

@@ -1,9 +1,12 @@
 require 'chef/knife'
 require 'chef/knife/base_vsphere_command'
+require 'chef/knife/search_helper'
 
 # List the disks attached to a VM
 # VsphereVmdisklist extends the BaseVspherecommand
 class Chef::Knife::VsphereVmDiskList < Chef::Knife::BaseVsphereCommand
+  include SearchHelper
+
   banner 'knife vsphere vm disk list VMNAME'
 
   common_options
@@ -18,9 +21,7 @@ def run
       fatal_exit 'You must specify a virtual machine name'
     end
 
-    vim_connection
-    vm = get_vm(vmname)
-    fatal_exit "Could not find #{vmname}" unless vm
+    vm = get_vm_by_name(vmname) || fatal_exit("Could not find #{vmname}")
 
     disks = vm.config.hardware.device.select do |device|
       device.is_a? RbVmomi::VIM::VirtualDisk