use return error handling in SetupRootless

There is no good reason to use logrus and os.Exit() here, other parts of
this function already return the error so do the same. The main podman
process will exit then with the normal formatted error message.

And also log an error about the last return which should never happen as
we should have exited above if the re-exec worked or errored out.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

pkg/domain/infra/abi/system_linux.go

@@ -59,6 +59,8 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, noMoveProcess bool,
 				}
 			}
 		}
+
+		// return early as we are already re-exec or root here so no need to join the rootless userns.
 		return nil
 	}
 
@@ -81,8 +83,7 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, noMoveProcess bool,
 	// if there is no pid file, try to join existing containers, and create a pause process.
 	ctrs, err := ic.Libpod.GetRunningContainers()
 	if err != nil {
-		logrus.Error(err.Error())
-		os.Exit(1)
+		return err
 	}
 
 	paths := []string{}
@@ -99,11 +100,12 @@ func (ic *ContainerEngine) SetupRootless(_ context.Context, noMoveProcess bool,
 		}
 	}
 	if err != nil {
-		logrus.Error(fmt.Errorf("invalid internal status, try resetting the pause process with %q: %w", os.Args[0]+" system migrate", err))
-		os.Exit(1)
+		return fmt.Errorf("invalid internal status, try resetting the pause process with %q: %w", os.Args[0]+" system migrate", err)
 	}
 	if became {
 		os.Exit(ret)
 	}
+
+	logrus.Error("Internal error, failed to re-exec podman into user namespace without error. This should never happen, if you see this please report a bug")
 	return nil
 }