munge spaces when generating CLI interface

## Expected Behavior
Validation shouldn't be passed

## Actual Behavior
Validation is passed

## Workflow Code
```
cwlVersion: v1.0
class: CommandLineTool

baseCommand: [echo]

inputs:
some string:
type: string
inputBinding:
position: 1

outputs: []
```

Tool usage looks like this and it says that `--some string` is an argument name
```
usage: test.cwl [-h] --some string SOME STRING [job_order]
test.cwl: error: argument --some string is required
```

But of course this doesn't work this way:
```
cwltool test.cwl --some string abcdef
------
[Errno 2] No such file or directory: '/mnt/projects/ASIL/pipelines/torrent-cwl-pipeline/abcdef'
```

But surprisingly works this way:
```
cwltool test.cwl --some string
--------
[job test.cwl] /tmp/tmpzbyAR6$ echo \
string
string
[job test.cwl] completed success
{}
Final process status is success
```

**Maybe some general constraints on id's value, are needed. Now its value is just a` string` as in doc or format, however there spaces are possible, and in id I think it's reasonable to avoid them**

## Your Environment
* cwltool version: 1.0.20170803160545

Start by reproducing the issue with the provided CommandLineTool workflow and inspect how its input IDs become CLI arguments. Verify the generated usage and invocation behavior for the `some string` input. Done means spaces in the input ID no longer produce the shown argument ambiguity or incorrect validation behavior.

Written by the indexing model from the issue text.