Test script runners refactoring

[mnaamani]

Problem: Too many confusing variables, and scripts to run integration tests.

Solution:

• A bit of house keeping.
• Dropped the REUSE_KEYS environment variable. When a scenario is run and output.json is found, the generated keys will be loaded from it.
• Updated scripts to explicitly remove output.json where appropriate. eg. when scenario is run to initialize a new network.
• Adding a new scenario called flow which can be used to run an individual flow. This allows us to more flexibly run flows without need to group them in a scenario.
• Changed default behavior of yarn test and yarn start to start a test chain (TESTING runtime profile)

[zeeshanakram3]

Looks good, just a few comments:

• In the Github workflows we still use yarn build:packages, maybe better to replace with yarn build for consistency?
• We should also remove run-test-node-docker.sh script too, it only exporting RUNTIME_PROFILE=TESTING , maybe do that in the calling script?

[zeeshanakram3]

LGTM