Fixing old tests and adding new ones for new code.

testdata/single_plugin.toml

@@ -0,0 +1,12 @@
+[kafka]
+  topic = "topic_with_metrics"
+  consumerGroupName = "telegraf_metrics_consumers"
+  zookeeperPeers = ["test.example.com:2181"]
+  batchSize = 1000
+  pass = ["some", "strings"]
+  drop = ["other", "stuff"]
+  interval = "5s"
+  [kafka.tagpass]
+    goodtag = ["mytag"]
+  [kafka.tagdrop]
+    badtag = ["othertag"]