What

This MR adds a safeguard for the snapshot script to cleaup temporary files in case of error.

Why

To check if the trap works you need to simulate a failoure. Instead of running the script itself, you can run this mockup:

#!/bin/sh

touch /tmp/file

trap 'rm -f /tmp/file' EXIT

echo "This is a test."

exit 1

echo "This won't be reached if an error occurs."

Document the interface of any function added or modified (see the coding guidelines)
Document any change to the user interface, including configuration parameters (see node configuration)
Provide automatic testing (see the testing guide).
For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
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