Easy generation of demo NSD & VNFDs

[stefanbschneider]

For demos (e.g., at the Y1 review), we'll use services like the ones from upb-emulator-mano-integration-demo or upb-containernet-emulator-summerschool-demo:

User --> Squid proxy --> Socat L4FW --> Apache webserver

For a demo, the descriptorgen should be able to generate descriptors for all VNFs and the complete NS place them in a project folder together with project.yaml. The following steps are still needed:

• [x] Probably don't need monitoring parameters
• [x] Allow referencing VM image (string) and format (drop-down) for each VNF
• [x] Optionally use locally stored default NSD and VNFD rather than fetching them from the tng-schema repository. This is useful to quickly adjust these default NSDs during a demo.
• [x] Generate project structure
• [x] Test the generated descriptors with the service platform to check if they really work (integration env)

[stefanbschneider]

Comparing current default VNFD/NSD on tng-schema and these example descriptors:

NSD looks similar (just slightly different names for connection points, eg, "ns:input" instead of "input")

VNFD:

• No monitoring parameters in the example --> may be removed from the default VNFD
• The example uses docker images from Dockerhub --> allow specifying such images with the descriptorgen
• descriptorgen: Fixed resource requirements for each VDU --> can easily be adjusted after generation
• Different names of VDU connection points --> shouldn't matter