Fix typo in mininet driver

Change-Id: Ifbfb39ed831ce76e9718ed2d470bf8269db326d2
diff --git a/TestON/drivers/common/cli/emulator/mininetclidriver.py b/TestON/drivers/common/cli/emulator/mininetclidriver.py
index 25cafe0..580b3b5 100644
--- a/TestON/drivers/common/cli/emulator/mininetclidriver.py
+++ b/TestON/drivers/common/cli/emulator/mininetclidriver.py
@@ -153,7 +153,7 @@
                     # Sudo asking for password
                     main.log.info( self.name + ": Sending sudo password" )
                     self.handle.sendline( self.pwd )
-                    i = self.handle.expect( [ '%s:' % self.user,
+                    i = self.handle.expect( [ '%s:' % self.user_name,
                                               self.prompt,
                                               pexpect.EOF,
                                               pexpect.TIMEOUT ],