Fix in fuel cli docmentation required and optional arguments

User expected to see in command help, not only optional arguments, but also required, for example --env.

[root@fuel product]# python fuel_cli_testing deploy -h
usage: fuel [global optional args] deploy [-h]

optional arguments:
  -h, --help show this help message and exit
[root@fuel product]# python fuel_cli_testing health -h
usage: fuel [global optional args] health [-h] [-l] [--check CHECK]

optional arguments:
  -h, --help show this help message and exit
  -l, --list List all available checks
  --check CHECK Run check for some id.

Also in global docs, you can see --env parameter as optional
1. it is not global parameter
2. it is not optional in some cases

[root@fuel product]# python fuel_cli_testing -h
usage: fuel [optional args] <namespace> [action] [flags]

optional arguments:
  -h, --help show this help message and exit
  --env ENV, --env-id ENV
                        environment id