Fix publicPath to be windows compatible

[gfdickinson]

This PR contains a:

• [X ] bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

When requiring html templates that were loaded with html-loader and then file-loader, the url that was generated was not compatible with windows machines. The path.join was changing the '/' into a ''.

Breaking Changes

N/A

Additional Info

[jsf-clabot]

All committers have signed the CLA.

[chriscasola]

@michael-ciniawsky could we get this merged?

This actually doesn't fix the issue for me on windows, but I think something like this might:

webpackOptions.output.publicPath = path.join('absolute', os.tmpdir(), '_karma_webpack_', publicPath, '/');

[gfdickinson]

@chriscasola how does your version with 'absolute' joined on the path fix things?

[matthieu-foucault]

Please undo the changes in files other than src/karma-webpack.js.

The actual change looks good to me.

[ryanclark]

@chriscasola can you confirm if this change/your change works on Windows (I'm unable to test), if so I agree with @matthieu-foucault

[matthieu-foucault]

I don't understand @chriscasola 's version. publicPath is a URL, not a filesystem path, and thus shouldn't be built using path.join

[matthieu-foucault]

Closing in favor of #373