Refactor provisionerd_tests.go to split provisionerd and runner tests

#2732 splits provisionerd package into `provisionerd` and `provisionerd/runner` packages, but leaves all the tests in `provisionerd_tests.go`

We should refactor the tests so that test cases for the runner are in a `runner_test.go` in the `runner` directory, and `provisionerd_tests.go` just tests the functionality in `provisionerd` itself.