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 ('').
Huh, this is on my Ubuntu Trusty running bash 4.3.11(1).

I just tested this on a CentOS 7 box with bash 4.2.45(1) and indeed, it works the way you have it and doesn't work the way I do...

Which makes me think this might be not really portable across versions of bash :-(

This one seems to work on both though:

```shell
$ SQ="'"
$ echo "master: ${x//\'/${SQ}${SQ}}"
master: aaaa''bbbbb''''cccc
$ cat <<EOF
> node: '${x//\'/${SQ}${SQ}}'
> EOF
node: 'aaaa''bbbbb''''cccc'
```

Do you think that's acceptable?