Control which test fields can be logged or not #2380
Description
Sending arbitrary test attributes to Logstash through the httpjson handler can be problematic if two tests define the same attribute differently. If the test A sends attribute x as an integer and this is indexed as such by Elastic, then if test B sends it as a string in the same index, the whole log record will be ignored. For this reason, I propose to provide a finer control in the framework as of which attributes can be logged or not. More specifically, we could add a loggable argument to the variable() definition that would control whether this attribute is going to be logged or not. By default, this should be set to False. Additionally, we should have a way to define loggable properties.
This feature should simplify also the logging implementation.