Reserved test nodes

[shibshib]

Description

This PR adds two flags to testnet nodes: reserved-nodes and reserved-only. These nodes serve to ensure that testnet nodes will only synchronize with the boot node, and no other nodes, this ensures that they won't lose their way if we have any issues with upgrades or bad blocks.

Type of Change

Additional flags

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation update
• [ ] Other (please describe):

Checklist

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have run cargo fmt and cargo clippy to ensure my code is formatted and linted correctly
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[sam0x17]

I went a head and added this to development in #409