ENH: Handle PBSPro message when job completed

[gjcooper]

Changes proposed in this pull request

• PBSPro version listed below does not return Unknown Job Id when a job has finished to stderr, instead it returns a message to stderr saying that the job has finished, recommending a command to access completed job details.
• This means that the _is_pending command continually reruns every 2 seconds (waiting for the job to complete)
• the fix for this is to check explicitly for the job finished message, and pass along that the job is no longer pending.

$ qstat --version
pbs_version = PBSPro_13.1.0.160576

All tests passed successfully with make check_before_commit

[codecov-io]

Codecov Report

Merging #2051 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2051      +/-   ##
==========================================
- Coverage   72.17%   72.16%   -0.01%     
==========================================
  Files        1134     1134              
  Lines       57098    57102       +4     
  Branches     8179     8180       +1     
==========================================
  Hits        41210    41210              
- Misses      14602    14606       +4     
  Partials     1286     1286

Flag	Coverage Δ
#smoketests	72.16% <0%> (-0.01%)	⬇️
#unittests	69.77% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
nipype/pipeline/plugins/pbs.py	17.14% <0%> (-1.04%)	⬇️

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