tests: skip a detailed exit status in test-lfs-test-server The mode of failure here differs between `lfs-test-server` and `hg serve`, and they each throw a different exception. The `hg serve` case raises a subclass of `StorageError`, which gets a detailed status. The `lfs-test-server` case raises a subclass of `Abort`, which does not. Since the exit code isn't currently conditionizable in the tests, this is the simplest way to avoid the failure. Differential Revision: https://phab.mercurial-scm.org/D9836