Input of array of enum is not recognized by the cwltool command line input object feature

If an input is defined as an array of enum, cwltool is unable to make a command line argument from it:

```
inputs:
applications:
type:
- type: array
items:
type: enum
symbols:
- a
- b
inputBinding:
itemSeparator: ","
prefix: --applications
```

## Expected Behavior
`cwltool --debug https://raw.githubusercontent.com/esanzgar/webservice-cwl/master/docker_cwls/array_enum.cwl --application a --application b` should feed `--applications a,b` to the tool.

## Actual Behavior
```
cwltool --debug https://raw.githubusercontent.com/esanzgar/webservice-cwl/master/docker_cwls/array_enum.cwl --application a --application b

Can't make command line argument from [ordereddict([('type', 'array'), ('items', ordereddict([('type', 'enum'), ('symbols', [u'https://raw.githubusercontent.com/esanzgar/webservice-cwl/master/docker_cwls/array_enum.cwl#applications/a', u'https://raw.githubusercontent.com/esanzgar/webservice-cwl/master/docker_cwls/array_enum.cwl#applications/b']), ('name', u'applicationsbf7fee68-a1f1-410b-a430-39c74fc57643')]))])]
usage: https://raw.githubusercontent.com/esanzgar/webservice-cwl/master/docker_cwls/array_enum.cwl
[-h] [job_order]
https://raw.githubusercontent.com/esanzgar/webservice-cwl/master/docker_cwls/array_enum.cwl: error: unrecognized arguments: --application --application b
```

## Workflow Code
```
cwltool --debug https://raw.githubusercontent.com/esanzgar/webservice-cwl/master/docker_cwls/array_enum.cwl --application a --application b
```

## Your Environment
* cwltool version: 1.0.20170928192020