Update previous results dictionary using the update_metrics method.
It calls metric_source.query_list to get a list of results (similar to discover()) then for each line in the response it updates results dictionary.
New results may be appeneded depending on the do_append parameter (True by default).
Previously, with prometheous, each metric.update called query_list resulting in O(n^2) when all metric were updated, like in the scylla_top dtest - causing test timeout when testing debug build.
(E.g. dtest-debug/216/testReport/scyllatop_test/TestScyllaTop/default_start_test/)
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