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 ('').
What version of bash are you running?  I tried this with bash 3 and bash 4 and it works for me.

```bash
$ x="aaaa'bbbbb''cccc"
$ cat <<EOF
> node: '${x//\'/''}'
> EOF
node: 'aaaa''bbbbb''''cccc'
```

According to the YAML spec, everything is ignored in single quotes except for a double single quote.