Added exit code 1 for cases when script failed to create backup

[itvexesme]

It allows handle backup.sh script execute issues when running from other scripts.

[CLAassistant]

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[dlen]

Thanks for your contribution @itvexesme! I think it would be more convenient to add a set -e instead of an exit 1
If you are up to modify your PR I'll merge it.

[itvexesme]

@dlen As far as I understand set -e logic, it will omit all output by echo about the reason of the issue, that is not quite right.

[dlen]

Yeah you are right with the current implementation of the script adding set -e does not make sense unless you want to refactor it into trapping signals.

Thanks!