No DockerCommandLineJob when use_container=False
No DockerCommandLineJob when use_container=False

Avoids using a Docker command line when `--no-container` passed.
This avoids creating an invalid Docker command line (with `None` as the
image). I believe this is a regression from here:

https://github.com/common-workflow-language/cwltool/commit/a91c16c343edf9ff7f52e3374ec1dfefe3d23799#diff-29ce315cc581b507c2832e379ce71ad6R175

cc @tetron

SciDAP/cwltool,common-workflow-language/cwltool,SciDAP/cwltool,common-workflow-language/cwltool,common-workflow-language/cwltool,SciDAP/cwltool,dleehr/cwltool,dleehr/cwltool,SciDAP/cwltool,dleehr/cwltool,dleehr/cwltool