Fixed ClearMLLogger to retrieve current task before trying to create a new one.

[H4dr1en]

Fixes #2343

Description: ClearMLLogger tries to retrieve current task before trying to create a new one.

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[vfdev-5]

@H4dr1en thanks for the PR ! Do you think we can write a distributed test for checking that everything is working ?

[H4dr1en]

@vfdev-5 This might be very tricky to test: we want to make sure that the communication between the subprocesses and the main process works well, so that clearml can log successfully in the clearml-server. I have now idea how to test that :D

Especially since there is no error to catch, this happens silently in the background

[vfdev-5]

@H4dr1en thanks a lot for the PR !
For the tests I agree that this could be a bit tricky to write and there is no error to catch.
Let's merge this like that and if possible to add a test we can do that later in a follow-up PR.
I still would like to hear from ClearML team.
@bmartinn could you please review as well. Thanks !

EDIT: There is a lint to fix and TPU tests are unrelated