Avoid potentially slow ws server slowing down live handler as well

[Martchus]

After moving the code for dealing with the live view image streaming to the live handler we should avoid blocking calls in that code because the live handler is not using multiple processes.

Tested by running a test locally and observing that the live_log file in the pool directory is created/removed as expected. The unit test has also been extended to cover the error case as well.

Related ticket: https://progress.opensuse.org/issues/163757

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.44%. Comparing base (3f4dbfd) to head (b664d39).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5766 +/- ## ========================================== + Coverage 98.43% 98.44% +0.01% ========================================== Files 393 393 Lines 38615 38632 +17 ========================================== + Hits 38012 38033 +21 + Misses 603 599 -4 ```

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