autopkgtest: use the quiet mode as for travis and co

Git-Dch: Ignore

debian/tests/run-tests

@@ -19,4 +19,4 @@ APT_INTEGRATION_TESTS_INTERNAL_SOLVER=/usr/lib/apt/solvers/apt \
 APT_INTEGRATION_TESTS_DUMP_SOLVER=/usr/lib/apt/solvers/dump \
 APT_INTEGRATION_TESTS_BUILD_DIR=/usr/bin \
 APT_INTEGRATION_TESTS_LIBRARY_PATH=/dev/null/does/not/exist \
-./test/integration/run-tests
+./test/integration/run-tests -q