HMI sends UI.Alert response earlier than TTS.Alert during processing two Alert requests

[VjKlepikov]

Description:
HMI sends UI.Alert response earlier than TTS.Alert during processing two Alert requests
Note: Issue is applicable for Alert and SubtleAlert RPCs

Occurrence: 100%

Preconditions:

1. Start WebHMI and SDL
2. Connect mobile device and consent it
3. Register app from mobile device
4. Activate the app

Steps to reproduce:

1. Send SubtleAlert request from the app
2. Send another SubtleAlert request from the app during the duration of displaying of SubtleAlert RPC from the previous step

Expected result:
HMI responds with code 4 to requests related to the second SubtleAlert request,
HMI send response to UI part only after sending response to TTS part
HMI -> SDL: {"error":{"code":4,"message":"TTS in progress. Rejected.","data":{"method":"TTS.Speak"}}}
HMI -> SDL: {"error":{"code":4,"message":"another SubtleAlert is active","data":{"method":"UI.SubtleAlert"}}}

Observed behavior:
HMI sends UI.Alert response earlier than TTS.Alert during processing two Alert requests
HMI -> SDL: {"error":{"code":4,"message":"another SubtleAlert is active","data":{"method":"UI.SubtleAlert"}}}
HMI -> SDL: {"error":{"code":4,"message":"TTS in progress. Rejected.","data":{"method":"TTS.Speak"}}}

Environment:
HMI: https://github.com/smartdevicelink/sdl_hmi/tree/develop (3bbcd28)
SDL: https://github.com/LuxoftSDL/sdl_core (7af6696)
Mobile App: SPT 20201023

[Jack-Byrne]

Fixed by #464