tests: tune flaky tests that error in travis occasionally

[holiman]

This PR fixes a couple of testcases that from time to time error on travis.

--- FAIL: TestInvalidNumberAnnouncement63 (0.06s)
    fetcher_test.go:628: peer with invalid numbered announcement not dropped

--- FAIL: TestEmptyWorkEthash (1.06s)
    worker_test.go:228: new task timeout

--- FAIL: TestReporter (0.04s)
    reporter_test.go:69: Expected counter to be 12, but is 0

--- FAIL: TestProtocolHook (0.02s)
    protocol_test.go:273: Expected peer ID to be set correctly, but it is not

Mostly it's timeouts, but there's one change in protocol_test.go that is changed 'semantically'.
The test expects a certain order of events, and sometimes it seems to arrive in a different order. I changed the test to accept any order, but I'm not sure if that is a false positive or an actual error that should be fixed somewhere.

The test comes from #17951 by @holisticode , PTAL