Use pin_memory=True, shuffle=True and num_workers=0 by default

[akihironitta]

What does this PR do?

This change has been suggested in #676 (comment).

This PR changes the default values of datamodules to:

• pin_memory=True
• shuffle=True
• num_workers=0 (Same as the default value of Dataloader in PyTorch: https://pytorch.org/docs/stable/data.html)

Before submitting

• [Add EMNISTDataModule #676] Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
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• Did you make sure your PR does only one thing, instead of bundling different changes together?
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• Did you write any new necessary tests? [not needed for typos/docs]
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PR review

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[codecov]

Codecov Report

Merging #701 (da383b9) into master (fb558d1) will increase coverage by 46.64%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #701       +/-   ##
===========================================
+ Coverage   24.83%   71.48%   +46.64%     
===========================================
  Files         119      119               
  Lines        7332     7332               
===========================================
+ Hits         1821     5241     +3420     
+ Misses       5511     2091     -3420     

Flag	Coverage Δ
cpu	71.48% <ø> (+46.64%)	⬆️
pytest	71.48% <ø> (+46.64%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pl_bolts/datasets/imagenet_dataset.py	19.65% <0.00%> (+1.15%)	⬆️
pl_bolts/datasets/kitti_dataset.py	34.61% <0.00%> (+1.92%)	⬆️
pl_bolts/callbacks/vision/confused_logit.py	26.02% <0.00%> (+4.10%)	⬆️
pl_bolts/callbacks/printing.py	71.18% <0.00%> (+6.77%)	⬆️
pl_bolts/models/rl/common/cli.py	11.76% <0.00%> (+11.76%)	⬆️
pl_bolts/models/self_supervised/amdim/datasets.py	56.89% <0.00%> (+12.06%)	⬆️
pl_bolts/optimizers/lr_scheduler.py	80.48% <0.00%> (+12.19%)	⬆️
pl_bolts/callbacks/byol_updates.py	68.18% <0.00%> (+22.72%)	⬆️
...s/models/detection/components/_supported_models.py	100.00% <0.00%> (+28.57%)	⬆️
pl_bolts/models/detection/faster_rcnn/backbones.py	92.30% <0.00%> (+30.76%)	⬆️
... and 60 more

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[akihironitta]

The failing tests are irrelevant to the change in this PR.