Fullnode rpc to exit with unsafe config

[aeyakovenko]

Problem

Leader failure fault tolerance for an in-process LocalCluster requires the node to expose an exit mechanism via an RPC. This mechanism is only available with the JsonRpcConfig::Unsafe fullnode option.

Summary of Changes

• Config option to guard availability of the exit rpc
• test to check that default is safe
• test to verify nodes exit and fails to exit with the safe config
• pass an exit signal from the fullnode through to TPU and TVU

Fixes #

[codecov]

Codecov Report

Merging #3082 into master will decrease coverage by 0.3%.
The diff coverage is 70%.

@@           Coverage Diff            @@
##           master   #3082     +/-   ##
========================================
- Coverage    78.5%   78.1%   -0.4%     
========================================
  Files         136     137      +1     
  Lines       19944   20134    +190     
========================================
+ Hits        15660   15744     +84     
- Misses       4284    4390    +106

[garious]

Can you find a better term than "unsafe"? Rust uses that term for the user to communicate to the compiler "your memory-safety rules are too conservative, back off, I got this".

[aeyakovenko]

@garious, debug seems to benign. A super safe way to do this would be to have 1 config item per “unsafe” test. So I could call this DebugRpcFullnodeExit

[garious]

sure or "TestOnly"

[mvines]

I'd rather the flag be very specific, DebugEnableRpcFullnodeExit, or something. This avoids creating a generic home for people to later sneak in other unrelated flags.

But this change overall is great, once it lands I'll expose it as a flag to the fullnode program since I'd like to use it in the bash integration tests and network deployment scripts

[garious]

Just the naming nit