Implement INT pipeline on v1model and ptf tests

[JonghwanHyun]

Based on the example transit code in the spec, I implemented INT pipeline against v1model.

• Implemented INT source, sink and transit functions.
• Run on v1model
• Compliant with spec v1.0
• PTF test codes for source, sink and transit functions.
• Tested on BMv2

[jklr]

@JonghwanHyun Thanks for the PR! Can we start by changing the directory structure? Let's create two sub directories under code:

• telemetry/code/p4src
• telemetry/code/tests

[jklr]

Closing this Pull Request for now as we're moving onto v2.0.