Revert "Refactor SessionPool"

This reverts commit 50057f59.
2 jobs for master in 5 minutes and 21 seconds (queued for 1 minute and 7 seconds)
Status Job ID Name Coverage
  Build
failed #72332
build_clazy_clang_tidy

00:01:46

failed #72331
linux kf5-qt5 qt5.12

00:03:35

 
Name Stage Failure
failed
build_clazy_clang_tidy Build
    return self.do_open(http.client.HTTPSConnection, req,
File "/usr/lib64/python3.8/urllib/request.py", line 1353, in do_open
raise URLError(err)
urllib.error.URLError: <urlopen error [Errno -3] Temporary failure in name resolution>
Uploading artifacts for failed job
Uploading artifacts...
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1
failed
linux kf5-qt5 qt5.12 Build
    return self.do_open(http.client.HTTPSConnection, req,
File "/usr/lib64/python3.8/urllib/request.py", line 1353, in do_open
raise URLError(err)
urllib.error.URLError: <urlopen error [Errno -3] Temporary failure in name resolution>
Uploading artifacts for failed job
Uploading artifacts...
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1