Fix short descriptions of neoctl & neomigrate in their headers

neo/scripts/neoctl.py

 #!/usr/bin/env python
 #
-# neoadmin - run an administrator node of NEO
+# neoctl - command-line interface to an administrator node of NEO
 #
 # Copyright (C) 2009-2019  Nexedi SA
 #

neo/scripts/neomigrate.py

 #!/usr/bin/env python
 #
-# neomaster - run a master node of NEO
+# neomigrate - import/export data between NEO and a FileStorage
 #
 # Copyright (C) 2006-2019  Nexedi SA
 #

neoctl

 #! /usr/bin/env python
 #
-# neoadmin - run an administrator  node of NEO
+# neoctl - command-line interface to an administrator node of NEO
 #
 # Copyright (C) 2009  Nexedi SA
 #