Cleanup and refactor code in service_chain_test.cc

Following changes have been implemented:

- Use using instead of using namespace
- Add and use helper methods for creating peers and configuring chains
- Add and use helper methods for verfification of routes and paths
- Minimize use of task_util::WaitForIdle

Change-Id: I33ccdb0b988fec768bb5c44b1de5d5c91fdd8bb3