add a defaults for integration.sh (#17709)

* add a default test image (ansible/ansible:centos7)
* add a default test target (all)

test/utils/shippable/integration.sh

@@ -2,10 +2,10 @@
 
 source_root=$(python -c "from os import path; print(path.abspath(path.join(path.dirname('$0'), '../../..')))")
 
-test_image="${IMAGE}"
+test_image="${IMAGE:-ansible/ansible:centos7}"
 test_privileged="${PRIVILEGED:-false}"
 test_flags="${TEST_FLAGS:-}"
-test_target="${TARGET:-}"
+test_target="${TARGET:-all}"
 test_ansible_dir="${TEST_ANSIBLE_DIR:-/root/ansible}"
 test_python3="${PYTHON3:-}"