Extend nomination monte carlo simulations to analyze timeouts (#4574)

# Description

Closes #4561

This change adds a couple more tests to the nomination tests for the
following scenarios:
1. Asymmetric quorums
2. Unresponsive validators

It also removes some protocol gating in the test suite that's no longer
necessary now that P22 is the current protocol in the build.

# Checklist
- [x] Reviewed the
[contributing](https://github.com/stellar/stellar-core/blob/master/CONTRIBUTING.md#submitting-changes)
document
- [x] Rebased on top of master (no merge commits)
- [x] Ran `clang-format` v8.0.0 (via `make format` or the Visual Studio
extension)
- [x] Compiles
- [x] Ran all tests
- [ ] If change impacts performance, include supporting evidence per the
[performance
document](https://github.com/stellar/stellar-core/blob/master/performance-eval/performance-eval.md)