Since nixpks 20.09, the test output is just an empty directory.
Restore saving the log output and linking to the driver.
Without linking to the driver, the driver is eligible for
garbage collection after running a test via `run-tests.sh --out-link-prefix`,
which implies lengthy driver rebuilds.
This improves debugging and experimenting by making it easy to compose fine-grained
scenarios that have specific tests and features enabled.
The VM test output now includes the subtest name and duration.
Remove the 'raise Exception()' hack for interactive mode.
Run 'banlist-and-restart' test before 'backups'. This speeds up the test
by avoiding an extra shutdown of all bitcoin-related services.
