Package-specific test timeouts

debci needs a method with which long-running test suites get a higher --timeout-test than the global default.

Currently, test timeout is set globally at 5h, being the maximum for existing tests. However, this negatively affects tests which encounter infinite loops: they block the test runner for the entire time.

We need a way to inform debci of package-specific timeouts.

As discussed in this debian-ci thread, this cannot be package-specific: it has to be host-specific, because hosts can have vastly different performance characteristics.