setup.py: log test returncode from VM

I'm seeing some spurious failures on Travis where the tests pass in the
VM but setup.py reports that they failed. Log the returncode that
setup.py sees to narrow down the issue.

Author: osandov

setup.py

@@ -180,15 +180,14 @@ def _run_vm(self, **kwds):
                 ]
                 if self.verbose:
                     args.append("-v")
-                return (
-                    vm.run(
-                        args, cwd=os.getcwd(), env={"DRGN_RUN_LINUX_HELPER_TESTS": "1"}
-                    ).returncode
-                    == 0
-                )
+                returncode = vm.run(
+                    args, cwd=os.getcwd(), env={"DRGN_RUN_LINUX_HELPER_TESTS": "1"}
+                ).returncode
         except vmtest.vm.LostVMError as e:
             self.announce(f"error: {e}", log.ERROR)
             return False
+        self.announce(f"Tests in VM returned {returncode}", log.INFO)
+        return returncode == 0
 
     def run(self):
         import vmtest.build