Improve device connection string placeholder text

Author: kgremban

articles/iot-edge/includes/iot-edge-register-device-symmetric.md

@@ -120,7 +120,7 @@ You should see JSON output in the console, similar to the following:
 
 ```json
 {
-  "connectionString": "HostName=my-iot-hub.azure-devices.net;DeviceId=my-edge-device-1;SharedAccessKey=saQ52bt6BBUlRfusqWuxPMAx4ysQwWEb5+1eidwzHPY="
+  "connectionString": "HostName=[hub_name].azure-devices.net;DeviceId=[device_id];SharedAccessKey=[device_key]"
 }
 ```
 

articles/iot-hub-device-update/device-update-raspberry-pi.md

@@ -135,7 +135,7 @@ Read the license terms prior to using the agent. Your installation and use const
            "runas": "adu",
            "connectionSource": {
               "connectionType": "string",
-              "connectionData": "HostName=example-connection-string.azure-devices.net;DeviceId=example-device;SharedAccessKey=M5oK/rOP12aB5678YMWv5vFWHFGJFwE8YU6u0uTnrmU=" 
+              "connectionData": "HostName=<hub_name>.azure-devices.net;DeviceId=<device_id>;SharedAccessKey=<device_key>" 
            },
            "manufacturer": "contoso",
            "model": "virtual-vacuum-v2"