Ability to use host / shell runtime in actions

[davidferlay]

Current

• Action commands can only be run in container defined in action.yalm

Expected

• Plugin commands should be able to be executed directly on host, using a kind of shell, as plugin actions do
• This will allow actions commands to embed and run pre-confirugured actions for instance

[lexbritvin]

WIP

1. Proper signal propagation to stop, kill, pause the actions, it's quite stable now. But ctrl+z may break execution, minor bug for me
2. Env variables substitution. Example

   script: |
     # Uses host environment variable during action compilation
     echo "${MY_HOST_ENV_VAR}" 
     # Result: echo "my host var"
   
     # Escape replacement with double $$, uses variable from script runtime
     echo "$${MY_LOCAL_ENV_VAR}" 
     # Result: echo "${MY_LOCAL_ENV_VAR}"
   
     # Use \$(...) for escaping inside an argument like in normal bash
     # Use \$$i to escape inside an argument and not replace $i with a host variable.
     bash -c "for i in \$(seq 60); do echo \$$i; sleep 1; done"
     # Result: bash -c "for i in \$(seq 60); do echo \$i; sleep 1; done"
   

   I tried to rework escape to be more user friendly, but it became overcomplicated. So I will leave it as is with $$, need to document it.
3. I played with current_bin variable to run sub actions. We may pass sensitive data like keyring passphrase to sub execution. As well as some other global flags like -vvvv. I investigated the secure ways to pass that. It may be a critical part to implement first to handle such cases easily without actions from user.