Add hadrian option for rerunning failed test

When you write a ghc patch and want to create a MR, you'd probably run all tests locally with hadrian/build -j --freeze1 test. You might run into a regression, where let's say T001, T002 and T003 fail. You write some code to fix the regression and now you manually have to copy down T001, T002 and T003.

It would be nicer, if hadrian, upon running all tests, created a file failed_tests which listed all the tests that previously failed and deletes them, when they pass again. Running them is also made easier with a flag --only-run-failed which only runs tests which previously failed. An example workflow could then look like

<write ghc code>
hadrian/build -j test
  - tests failed: A, B (failed_tests file has [A, B])
<write code to fix regression A>
hadrian/build -j --only-run-failed
  - tests failed: B (failed_tests file has [B])
<fix regression B, adding regression C>
hadrian/build -j --only-run-failed
  - all tests passed!
hadrian/build -j
  - tests failed: C (failed_tests file has [C])
<fix C>
hadrian/build -j
  - all tests passed!