test: Avoid input() in simple-agent.py.

That function reads a string of python code and immediately executes
it.  This required passphrases to be input as python literals, we
can just use a string as passphrase instead.

test/simple-agent

@@ -20,42 +20,20 @@ class Agent(dbus.service.Object):
         print("Release")
         mainloop.quit()
 
-    def input_passphrase(self):
-        response = {}
-
-        if not self.passphrase:
-            print("Service credentials requested, type cancel to cancel")
-            args = input('Answer: ')
-
-            for arg in args.split():
-                if arg.startswith("cancel"):
-                    response["Error"] = arg
-
-                if arg.startswith("Passphrase="):
-                    passphrase = arg.replace("Passphrase=", "", 1)
-                    response["Passphrase"] = passphrase
-        else:
-            if self.passphrase:
-                response["Passphrase"] = self.passphrase
-
-        return response
-
     @dbus.service.method("net.connman.iwd.Agent",
                             in_signature='o',
                             out_signature='s')
     def RequestPassphrase(self, path):
         print("RequestPassphrase (%s)" % (path))
 
-        response = {}
-        response.update(self.input_passphrase())
+        print("Service credentials requested, type cancel to cancel")
+        passphrase = raw_input('Answer: ')
 
-        if response.has_key("Error"):
-            if response["Error"] == "cancel":
-                raise Canceled("canceled")
-                return
+        if not passphrase or passphrase == 'cancel':
+            raise Canceled("canceled")
 
-        print("returning (%s)" % (response["Passphrase"]))
-        return response["Passphrase"]
+        print("returning (%s)" % (passphrase))
+        return passphrase
 
     @dbus.service.method("net.connman.iwd.Agent",
                             in_signature='', out_signature='')