improve error handling robustness for os.execvpe

see: pexpect/pexpect#512

Author: ryanpetrello

ptyprocess/ptyprocess.py

@@ -292,6 +292,11 @@ def spawn(
                 os.write(exec_err_pipe_write, tosend)
                 os.close(exec_err_pipe_write)
                 os._exit(os.EX_OSERR)
+            except Exception as err:
+                cls_name = err.__class__.__name__
+                os.write(exec_err_pipe_write, 'Exception:0:{}: {}'.format(cls_name, str(err)))
+                os.close(exec_err_pipe_write)
+                os._exit(os.EX_OSERR)
 
         # Parent
         inst = cls(pid, fd)