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 58.82353% with 7 lines in your changes missing coverage. Please review.

Project coverage is 86.66%. Comparing base (73cc79d) to head (bc70321).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...maker/modules/train/container_drivers/mpi_utils.py	58.82%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4966      +/-   ##
==========================================
+ Coverage   86.41%   86.66%   +0.24%     
==========================================
  Files         439      438       -1     
  Lines       42717    42535     -182     
==========================================
- Hits        36914    36863      -51     
+ Misses       5803     5672     -131     

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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)