Quote strings in bash populated YAML files.

Quoting is hard.  When writing strings into YAML files, wrap them in single quotes.  Also escape any embedded single quotes in those strings via a double signle quote ('').
I could also use sed here but I'd rather not shell out.
```bash
 cat <<EOF
> node: '$(echo "$x" | sed -e "s/'/''/g")'
> EOF
node: 'aaaa''bbbbb''''cccc'
```