Initializes job assuming Docker is available, still tries to run it if not

[tetron]

When setting up the job, paths are different depending on whether it will run inside a container or outside.

In CommandLineJob.run, if running in Docker is not available (docker.get_from_requirements returns None) it will try to run the job without Docker. However, because the job was already set up assuming Docker, this doesn't work.

[mr-c]

This is the root cause of #281 and #213

[kapilkd13]

I think one way to solve this problem is to check if Docker is available even before setting paths in Job. What do you think.