Mistral bash completion script optimization

Currently, mistral command completion command is available, after putting the tools/mistral.bash_completion script file to /etc/bash_completion.d/. However, the commands supportted by mistral is hardcoded in the script, which is not scalable and will not be easily maintained.

the blueprint will implement a helper command 'mistral bash-completion' to generate available commands and options, so that we could make bash completion script generated automatically.