[collectd] double-quotes and backslashes in Values index

[alex]

On Fri, May 16, 2014 at 01:06:40PM +0000, alex wrote:

>This metric configuration for F5 loadbalancers used to work well in
>5.0.0-1 (a backport for Ubuntu Lucid) but broke somehow in 5.4.0-3
>(another backport for Ubuntu precise)

I was able to narrow it down to the change from 5.1.0 to 5.2.0.

5.1.0 being still able to parse metrics with backslash+doublequoted
index in "values" and 5.2.0 failing and ignore such metrics.