tests: don't ignore shutdown hangs in failure injector

Previously, a hang on SIGINT would be logged, but then
the test would proceed with a node in this zombie state.

Since shutdown hangs are always a bug, it is correct to fail
the test as early as we can with the right reason, so just
re-raise the exception instead of trying to proceed.

Related: redpanda-data#5178

tests/rptest/services/failure_injector.py

@@ -40,12 +40,19 @@ def __enter__(self):
     def __exit__(self, type, value, traceback):
         self._heal_all()
 
-    def inject_failure(self, spec):
+    def inject_failure(self, spec, require_success=False):
         self.redpanda.logger.info(f"injecting failure: {spec}")
         try:
             self._start_func(spec.type)(spec.node)
         except Exception as e:
             self.redpanda.logger.info(f"injecting failure error: {e}")
+            if spec.type == FailureSpec.FAILURE_TERMINATE and isinstance(
+                    e, TimeoutError):
+                # A timeout during termination indicates a shutdown hang in redpanda: this
+                # is a bug and we should fail the test on it.  Otherwise we'd leave the node
+                # in a weird state & get some non-obvious failure later in the test, such
+                # as https://github.com/redpanda-data/redpanda/issues/5178
+                raise
         finally:
             if spec.length is not None:
                 if spec.length == 0: