test: Connect test unit to console when running interactively

When running interactively, let's connect the test unit directly
to the console. This enables adding "bash" anywhere within an
integration test to get a shell within the test environment.

(cherry picked from commit fe7413d1955bbf0f8fe869543c423025a22a4671)

test/integration-test-wrapper.py

@@ -456,6 +456,16 @@ def main() -> None:
             [Unit]
             Wants=multi-user.target getty-pre.target
             Before=getty-pre.target
+
+            [Service]
+            StandardInput=tty
+            StandardOutput=inherit
+            StandardError=inherit
+            TTYReset=yes
+            TTYVHangup=yes
+            IgnoreSIGPIPE=no
+            # bash ignores SIGTERM
+            KillSignal=SIGHUP
             """
         )