lisa.wa: Include classifiers in WAResultsCollector

Created by: mrkajetanp

Some workloads in workload-automation (e.g. jankbench) include a field in their results called 'classifiers'. It may contain the number of repetitions, the name of the subtest being ran or other information.

Currently, Lisa completely ignores this field leading to situations such as jankbench results not including the name of the test as it uses 'metric' for the data type (e.g. mean, std_dev etc.) and classifiers['test_name'] to keep the actual subtest name.

This patch includes classifiers expanded to separate columns in the df containing WAOutput results when they are present. When classifiers are not present or are empty, e.g. with pcmark, speedometer etc., the resulting df will not be affected by the change.