use [sys.exe, "-c", "…launch_new_instance()"] in launchers

instead of [sys.exe, module_path], which resulted in the modules being `__main__`, which caused problems.

IPython/parallel/apps/launcher.py

@@ -24,6 +24,7 b' import logging'
 import os
 import re
 import stat
+import sys
 import time
 
 # signal imports, handling various platforms, versions
@@ -60,8 +61,8 b' from IPython.utils.text import EvalFormatter'
 from IPython.utils.traitlets import (
     Any, Integer, CFloat, List, Unicode, Dict, Instance, HasTraits,
 )
-from IPython.utils.path import get_ipython_module_path, get_home_dir
-from IPython.utils.process import find_cmd, pycmd2argv, FindCmdError
+from IPython.utils.path import get_home_dir
+from IPython.utils.process import find_cmd, FindCmdError
 
 from .win32support import forward_read_events
 
@@ -73,18 +74,13 b" WINDOWS = os.name == 'nt'"
 # Paths to the kernel apps
 #-----------------------------------------------------------------------------
 
+cmd = "from IPython.parallel.apps.%s import launch_new_instance; launch_new_instance()"
 
-ipcluster_cmd_argv = pycmd2argv(get_ipython_module_path(
-    'IPython.parallel.apps.ipclusterapp'
-))
+ipcluster_cmd_argv = [sys.executable, "-c", cmd % "ipclusterapp"]
 
-ipengine_cmd_argv = pycmd2argv(get_ipython_module_path(
-    'IPython.parallel.apps.ipengineapp'
-))
+ipengine_cmd_argv = [sys.executable, "-c", cmd % "ipengineapp"]
 
-ipcontroller_cmd_argv = pycmd2argv(get_ipython_module_path(
-    'IPython.parallel.apps.ipcontrollerapp'
-))
+ipcontroller_cmd_argv = [sys.executable, "-c", cmd % "ipcontrollerapp"]
 
 #-----------------------------------------------------------------------------
 # Base launchers and errors