E2E Test scenario: Delegate stake

[leszko]

Create an E2E Test which covers the following scenario:

1. Start and register O1
2. Using a different ETH account, delegate stake
3. Wait for the next round and proceed with transcoding by the Orchestrator
4. Call reward
5. Check that LPT stake has increased and that ETH account received fees
6. Call withdraw stake and withdraw fees
7. Check account balance (LPT and ETH)

Additional comments

• The intention of this E2E Test is to verify that Livepeer node works correctly from the delegator's perspective
• If this scenario becomes too big in scope, consider splitting it into a few E2E test scenarios
• Some parts (registering orchestrator, performing transcoding) may be shared across multiple E2E Test scenarios
  • refactor them into reusable parts
  • check related issues:
    • #2319
    • #2421
    • #2422