Bubble up genesis load errors instead of exiting

[steviez]

Problem

Currently, the function open_genesis_config() performs several operations that could fail, and unwraps / exits immediately.

Summary of Changes

Bubble the error up to allow the caller to decide what to do with the result. solana-validator and solana-ledger-tool will essentially have unchanged behavior as they both exit if this result is bad. But, this change removes one more place that could kill the process

[codecov]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (6976b75) 81.7% compared to head (56f97ba) 81.7%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #34851     +/-   ##
=========================================
- Coverage    81.7%    81.7%   -0.1%     
=========================================
  Files         826      826             
  Lines      223168   223174      +6     
=========================================
- Hits       182446   182411     -35     
- Misses      40722    40763     +41     

[brooksprumo]

lgtm, thanks!