Support new command to wait for a job to finish

[pdellaert]

When you start a job, the job will run in the background. As a result, you have to check the job yourself to see if it is finished or not. And if it is finished, in what state

Proposed solution:

• Add a new command 'wait_for_job'
• Returns the full job object in case the job is finished
• If the job fails, the command fails as well
• The command will run and check every second if the Job has finished.

More information on the job entity to understand the different supported statuses:
https://nuagenetworks.github.io/vsd-api-documentation/v4_0/job.html