[SPARK-4291][Build] Rename network module project names

The names of the recently introduced network modules are inconsistent with those of the other modules in the project:

```
[INFO] Reactor Build Order:
[INFO] 
[INFO] Spark Project Parent POM
[INFO] Spark Project Common Network Code
[INFO] Spark Project Shuffle Streaming Service Code
[INFO] Spark Project Core
[INFO] Spark Project Bagel
[INFO] Spark Project GraphX
[INFO] Spark Project Streaming
[INFO] Spark Project Catalyst
[INFO] Spark Project SQL
[INFO] Spark Project ML Library
[INFO] Spark Project Tools
[INFO] Spark Project Hive
[INFO] Spark Project REPL
[INFO] Spark Project YARN Parent POM
[INFO] Spark Project YARN Stable API
[INFO] Spark Project Assembly
[INFO] Spark Project External Twitter
[INFO] Spark Project External Kafka
[INFO] Spark Project External Flume Sink
[INFO] Spark Project External Flume
[INFO] Spark Project External ZeroMQ
[INFO] Spark Project External MQTT
[INFO] Spark Project Examples
[INFO] Spark Project Yarn Shuffle Service Code
```

We should just drop the "Code" suffix since it doesn't sacrifice any meaning.