Sequential model parallel with multi nodes regarding --num_nodes

[haven-jeon]

What does this PR do?

Fixes #5312

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[codecov]

Codecov Report

Merging #5327 (33ffcbb) into master (ab7512d) will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #5327   +/-   ##
======================================
  Coverage      93%     93%           
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  Files         134     134           
  Lines        9950    9950           
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  Hits         9261    9261           
  Misses        689     689           

[Borda]

would be great to have a test for it too