Start actinia worker automatically on VM

[mmacata]

When actinia is configured with job type other than local, the job will be processed by an actinia worker. Currently there is no mechanism inside actinia to start the worker automatically, as there are many different options, where the worker can run (e.g. VM, kubernetes, HPC, ...) (For VM start see #401) Input / Output data need to be stored on mounted storage. Some ideas to keep it standardised, so that python API stays the same for actinia-job-receiver (here details for VM approach):

• prepare_actinia: VM starts, VM is installed (via ansible?) -> #401
• execute_actinia: job is passed to worker / worker is started
• goodbye_actinia: confirm that worker shut down correctly and that VM is shutdown as well and no data loss can occur -> #402

Also mind monitoring #403