What do these changes do?

• Adds missing optional force parameter to DockerVolume.delete().
• When deleting volumes in tests check that these no longer exist.

Are there changes in behavior for the user?

No user impact is expected.

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
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  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the changes folder
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    • .bugfix: Signifying a bug fix.
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