Add support for each power_state

Add the `power_state` computed attribute to to `r/virtual_machine` docs.

Signed-off-by: Ryan Johnson <[email protected]>

website/docs/r/virtual_machine.html.markdown

@@ -1639,6 +1639,8 @@ The following attributes are exported on the base level of this resource:
 * `vapp_transport` - Computed value which is only valid for cloned virtual
   machines. A list of vApp transport methods supported by the source virtual
   machine or template.
+* `power_state` - A computed value for the current power state of the virtual
+  machine. One of `on`, `off`, or `suspended`.
 
 [docs-about-morefs]: /docs/providers/vsphere/index.html#use-of-managed-object-references-by-the-vsphere-provider