devenv: switch OpenTSDB docker block (#17849)

old docker image, https://hub.docker.com/r/opower/opentsdb/,  seems to be gone

devenv/docker/blocks/opentsdb/docker-compose.yaml

@@ -1,5 +1,5 @@
   opentsdb:
-    image: opower/opentsdb:latest
+    image: petergrace/opentsdb-docker:latest
     ports:
       - "4242:4242"