[Backup] Return error when mariabackup or other backup steps fail

[EzxD]

Contribution Guidelines

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What does this PR include?

Short Description

Fixes #7144. backup_and_restore.sh exits with code 0 even when mariabackup fails, producing broken backups silently.

Two problems:

1. The mariabackup commands inside docker run are chained with ; (semicolons), so --prepare, chown, and tar all run even after --backup fails — creating a broken archive that looks valid.
2. None of the docker run backup commands have their exit codes checked.

This PR changes the mariabackup chain from ; to && and adds exit code checks for all backup steps. The script now exits with code 1 if any step failed.

Affected Containers

None — this only changes the host-side helper script helper-scripts/backup_and_restore.sh.

Did you run tests?

What did you tested?

Verified the shell logic that causes the bug:

# Old behavior (;) — all commands run, exit 0
/bin/sh -c "false ; echo 'prepare ran' ; echo 'tar ran'"
# Output: prepare ran / tar ran / exit code: 0

# New behavior (&&) — stops at failure, exit 1
/bin/sh -c "false && echo 'prepare ran' && echo 'tar ran'"
# Output: exit code: 1

Also ran bash -n syntax check on the modified script.

What were the final results? (Awaited, got)

With &&, the command chain stops at the first failure and propagates a non-zero exit code. The error tracking logic then catches it and exits the script with code 1. This matches the expected behavior described in #7144.