In supervised nodes, the Supervisor's NodeConfig$scripts vector adds scripts to
the end of the user-provided scripts (options.scripts_to_load), so they load
_after_ any user-provided ones. This can cause confusing redef pitfalls when
users expect their customizations to run last, as they normally do.
This adds two members in Supervisor::NodeConfig, `addl_base_scripts` and
`addl_user_scripts`, to store scripts to load before and after the user scripts,
respectively. The latter serves the same purpose as the old `scripts` member,
which is still there but deprecated (in scriptland only). It functions as
before, after any scripts added via `addl_user_scripts`.
* Generally increase timeouts for tests that have recent transient
failures
* Change any test that relied on `btest-bg-wait -k` since that's never
going to play with with CI systems. Instead, we always need to have
a well-defined termination condition in the test itself (and most
already did, so didn't really need the `-k` flag anyway).
