Update python cpu reporting (#552)

The scrypted web ui looks to be reading from `cpu`:
64f696599c/plugins/core/ui/src/components/plugin/PluginStats.vue (L67)
and is being published on the nodejs side as `cpu`:
227b287f1e/server/src/plugin/plugin-remote-worker.ts (L21)

Might need to change this as well?
cc43273f34/server/src/plugin/plugin-host.ts (L59)

server/python/plugin-remote.py

@@ -490,7 +490,7 @@ async def async_main(loop: AbstractEventLoop):
                     heapTotal = 0
             stats = {
                 'type': 'stats',
-                'cpuUsage': {
+                'cpu': {
                     'user': ptime,
                     'system': 0,
                 },