Simulated Backend State Transition Tests Part 1

[rauljordan]

This is part of #904

---

Description

This PR serves as the first instance of using our simulated backend to run YAML tests for pure state transitions of the beacon chain. This PR creates a StateTest category for YAML, and advances a beacon state by N slots given the following configuration:

title: Sample Ethereum Serenity State Transition Tests
summary: Testing state transitions occurring with no blocks being published
test_suite: prysm
fork: tchaikovsky
version: 1.0
test_cases:
  - config:
      publish_blocks: false
      epoch_length: 64
      deposits_for_chain_start: 1000
      num_slots: 32 # Testing advancing state to slot < EpochLength
    results:
      slot: 32
  - config:
      publish_blocks: false
      epoch_length: 64
      deposits_for_chain_start: 16384
      num_slots: 64 # Testing advancing state to exactly slot == EpochLength
    results:
      slot: 64
  - config:
      publish_blocks: false
      epoch_length: 64
      deposits_for_chain_start: 1000
      num_slots: 128 # Testing advancing state's slot == 2*EpochLength
    results:
      slot: 128

This PR only advances the state without including any blocks during each state transition instance.

Steps to Reproduce

go run ./beacon-chain/chaintest/main.go -tests-dir ./beacon-chain/chaintest/tests

[terencechain]

Looks good. No comment

[codecov]

Codecov Report

Merging #1221 into master will increase coverage by 0.09%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master    #1221      +/-   ##
==========================================
+ Coverage   73.06%   73.15%   +0.09%     
==========================================
  Files          86       85       -1     
  Lines        5825     5797      -28     
==========================================
- Hits         4256     4241      -15     
+ Misses       1221     1214       -7     
+ Partials      348      342       -6