Add this module's namespace to the 'module_' namespace.

Much like we currently have *setup* register the variable `module_setup`, we would like other facts-modules register their own namespace. This means that:

 - *network_facts* registers `module_network`
 - *hpilo_facts* registers `module_hw`
 - *vsphere_facts* registers `module_hw`

In retrospect, it would have made more sense to have `setup` register `module_ansible` instead as the setup module uses the `ansible_` namesepace.

Having the `module_` namespace allows us to check whether a certain namespace has already been loaded so we can avoid running the facts module a second time using only_if.

```yaml
 - action: network_facts host=${ansible_hostname_short}
   only_if: is_unset('$module_network')
```

library/hpilo_facts

@@ -124,7 +124,9 @@ def main():
 
     # TODO: Count number of CPUs, DIMMs and total memory
     data = ilo.get_host_data()
-    facts = {}
+    facts = {
+        'module_hw': True,
+    }
     for entry in data:
         if not entry.has_key('type'): continue
         if entry['type'] == 0: # BIOS Information

library/vsphere_facts

@@ -107,6 +107,7 @@ def main():
 
     data = vm.get_properties()
     facts = {
+        'module_hw': True,
         'hw_name': vm.properties.name,
         'hw_guest_full_name':  vm.properties.config.guestFullName,
         'hw_guest_id': vm.properties.config.guestId,