delay initialization of urllib3 connection pool and reset on fork

[beniwohli]

this should avoid re-use of the connection pool of the parent process
after a fork.

fixes #1373

What does this pull request do?

Related issues

closes #ISSUE

[ghost]

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• Start Time: 2021-11-05T13:56:56.715+0000

• Duration: 34 min 48 sec

• Commit: 4c01482

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Skipped	8977
Total	19128

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[basepi]

Nice find!

[basepi]

Can you add CHANGELOG before you merge this?

[ghost]

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• Start Time: 2021-11-08T16:06:31.975+0000

• Duration: 34 min 41 sec

• Commit: a9f1995

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Test	Results
Failed	0
Passed	10151
Skipped	8977
Total	19128

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Tests succeeded.

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