Renamed a variable to explain better what it is

findTaggedServiceIds does not return an array of tag attributes. It
returns an array of tags, each of them being an array of attributes.
This is necessary because a service can be tagged several times with
the same tag (useful when attributes are used to configure the 
behavior of the tag, like for kernel.event_listener for instance)
Merge pull request #1 from stof/patch-1

Renamed a variable to explain better what it is