Tweak names of tests and test files to make their purpose clearer

[maxalbert]

Related to my comment in #577, some of the tests and test files are quite generically named (or perhaps even slightly mis-named) so that the purpose of the tests isn't very clear. This may accidentally lead to the addition of tests that are either superfluous or don't actually test what they are supposed to tests.

In particular, the tests in integration_tests/tests/flowmachine_server_tests/test_action_*.py are supposed to test the various action handlers rather than any specific queries, but this is not apparent.

Similarly, it is not obvious that integration_tests/tests/test_queries.py exercises the queries through flowclient.

There are likely a few other such cases.