Use common functions for miner and it's tests #1421
Description
Rationale
Currently, miner (specifically miner/worker.go) has certain functions which are modified a bit for bor. We also have certain e2e tests in test_backend.go which have similar functions but with slightly different logic to introduce delays for testing.
Whenever a change is made in the miner module (either by us or through geth upstream), we might miss making those changes in the tests and they would still pass.
Implementation
Have some common functions which can be re-used for tests if possible. Or at least modify tests such that it breaks when something's wrong.