Fix ssh host policy

[sage-maker]

Issue #, if available: #4946

Description of changes: Change the SSH host policy to reject when missing

Testing done: Unit + integration

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[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.

Project coverage is 86.68%. Comparing base (10b64f6) to head (ce046d4).
Report is 116 commits behind head on master.

Files with missing lines	Patch %	Lines
...maker/modules/train/container_drivers/mpi_utils.py	88.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4966      +/-   ##
==========================================
+ Coverage   86.57%   86.68%   +0.11%     
==========================================
  Files         438      438              
  Lines       42584    42589       +5     
==========================================
+ Hits        36866    36918      +52     
+ Misses       5718     5671      -47     

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[benieric]

Pretty sure for this to work we will need to create some custom policy like:

class CustomHostKeyPolicy(paramiko.client.MissingHostKeyPolicy):
   def missing_host_key(self, client, hostname, key):
      # if hostname is like `algo-*` autoadd otherwise reject

client = paramiko.SSHClient()
client.set_missing_host_key_policy(CustomHostKeyPolicy)

[benieric]

Nice

[benieric]

If this assert has flaky results, the previous asserts should be sufficient

[benieric]

Thanks for this change @sage-maker !