Flaky test cases caused by Counter Enum

[jmazanec15]

Currently, the plugin uses KNNCounter enum to keep track of different counts. For example, GRAPH_QUERY_REQUESTS keeps track of the number of queries made to graphs on a single node.

Because Unit tests run in the same JVM, this can lead to flaky failures, where the counter is incremented by some action in one test, and the value is checked in another test.

In order to fix this issue, these counters should be reset before running unit tests.