cwl: troubles with partial workflow execution

[audrium]

Investigate why partial workflow execution no longer works as expected.

$ reana-client run -f ./reana-cwl.yaml -w partial -o TARGET=gendata
...
partial.1 has been queued

$ reana-client logs -w partial                                     
==> Workflow engine logs
Workflow exited unexpectedly.
Not found: 'TARGET'

Also:

$ reana-client restart -w partial -o TARGET=gendata
Cannot start workflow partial: 
==> ERROR: Operational option "--target" not supported.

Originally posted by @tiborsimko in #192 (comment)