Don't raise exception on inexistent services in 'down' command

When running 'podman-compose down <service>', if service is not part of
the compose, a KeyError exception was raised it function 'get_excluded'.

By only allowing evaluation of services that exist in the compose
provides a cleaner and gentler exit for this case.

Author: rjeffman

podman_compose.py

@@ -2600,7 +2600,8 @@ def get_excluded(compose, args):
     if args.services:
         excluded = set(compose.services)
         for service in args.services:
-            excluded -= set(x.name for x in compose.services[service]["_deps"])
+            if service in compose.services:
+                excluded -= set(x.name for x in compose.services[service]["_deps"])
             excluded.discard(service)
     log.debug("** excluding: %s", excluded)
     return excluded

tests/integration/test_podman_compose_up_down.py

@@ -89,3 +89,21 @@ def test_up(self, profiles, expected_services):
             actual_services[service] = service in actual_output
 
         self.assertEqual(expected_services, actual_services)
+
+    def test_down_inexistent_service(self):
+        try:
+            up_cmd = [
+                podman_compose_path(), "-f", profile_compose_file(), "up", "-d"
+            ]
+            self.run_subprocess_assert_returncode(up_cmd)
+        finally:
+            # run the test case
+            down_cmd = [
+                podman_compose_path(),
+                "-f",
+                profile_compose_file(),
+                "down",
+                "inexistent_service"
+            ]
+            # This run should succeed
+            self.run_subprocess_assert_returncode(down_cmd)