agent: launch commands and listen for stdout and stderr streams

[GridexX]

This is one of the second issue related to the agent.

For now we have defined the following tasks:

• Find how to retrieve stdout and stderr streams launched by a command with unshare
• Define the class CommandService (name can be changed) that will be called to launch a specific command with the code and retrieve the streams. It will
  • fork the process and launch commands based on the information retrieved
  • retrieve and return the outputs of the process

This is still an early proposal of the tasks to do. We need further exploring before truly having a grasp on what needs to be done. Please comment and discuss with us anything we missed or misunderstood, or if this does not look like a logical division of tasks.