Increment port when taken

[ZhaofengWu]

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• Did you write any new necessary tests?
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What does this PR do?

Fixes #2081. When a port is already taken and if we are under a pre-set retry limit, increment the port number and try again. In fact interestingly this missing functionality is currently mentioned in an in-line comment.
https://github.com/PyTorchLightning/pytorch-lightning/blob/bd49b07fbba09b1e7d8851ee5a1ffce3d5925e9e/pytorch_lightning/trainer/distrib_data_parallel.py#L426

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[codecov]

Codecov Report

Merging #2140 into master will decrease coverage by 0%.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master   #2140   +/-   ##
======================================
- Coverage      87%     87%   -0%     
======================================
  Files          68      68           
  Lines        5180    5188    +8     
======================================
  Hits         4508    4508           
- Misses        672     680    +8     

[williamFalcon]

ummm... we need to test this a bit more. i think it was there, then it was removed because it didn't work well. let's hash this out for 0.9.0

[mergify]

This pull request is now in conflict... :(

[williamFalcon]

@ZhaofengWu
Ok, i tried this way but it doesn't actually work. I'll add you as co-author to #2231 which does work (just tried it). I use a slightly different approach there.

[Borda]

@williamFalcon GH does not support anything like the co-author of a PR
the only way how to solve this situation is merge his PR to yours and keep his PR id in the changelog as I did here for example #1920 (comment)
well we mined co-authors once or twice to be listed as release contributors but it was too time demanding as I had to do it manually and manually pair mails and GH users so now we just list PR authors from the changelog
so I am adding this PR to the changelog next to yours, see #2181