argparser booleans without extra parameters

I've observed that --use_cuda or any other arg that use convert_boolean type requires passing one argument:

`python tts-api/server/server.py --use_cuda <true,1,yes> --debug <true,1,yes> `

It wouldn't be better if we use without args? Like:

`python tts-api/server/server.py --use_cuda --debug `