Fix/Enhance node management.

[BalaBalaYi]

What changes were proposed in this pull request?

1. Add 'deletion_timestamp' condition when judging whether there is another same pod running. To avoid mistakenly identifying the current pod(to be removed) as the target.
2. Still need judgement when there is 0 pod list from k8s.

Why are the changes needed?

Fix/Enhance node management.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

UT and training.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.42%. Comparing base (e88d7eb) to head (16cf7d1).

Files with missing lines	Patch %	Lines
dlrover/python/master/node/dist_job_manager.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1301      +/-   ##
==========================================
+ Coverage   80.40%   80.42%   +0.01%     
==========================================
  Files         222      222              
  Lines       20544    20553       +9     
==========================================
+ Hits        16518    16529      +11     
+ Misses       4026     4024       -2     

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