machines: Use iframe download workaround on all browsers
machines: Use iframe download workaround on all browsers

Chromium 65 refuses to download the generated .vv file as well now:

```
CDP: {"source":"other","level":"error","text":"Refused to frame '' because it violates the following Content Security Policy directive: \"default-src 'self' http://127.0.0.2:9091\". Note that 'frame-src' was not explicitly set, so 'default-src' is used as a fallback.\n","timestamp":1527156936689.5,"url":"http://127.0.0.2:9091/cockpit/$0021b50df7588e9af173d46d5eda7bdac26be09b97f000fec7a55dda9228c356/machines/machines.js","lineNumber":6126}
CDP: executionContextDestroyed 11
```

And after that one just gets a blank page with a sad face. Use the
workaround of wrapping this in a dynamic iframe on all browsers now.

Closes #9229

martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit,deryni/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,garrett/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,mvollmer/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,stefwalter/cockpit,moraleslazaro/cockpit,stefwalter/cockpit,mareklibra/cockpit,andreasn/cockpit,mvollmer/cockpit,cockpituous/cockpit,stefwalter/cockpit,cockpit-project/cockpit,andreasn/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit,andreasn/cockpit,cockpit-project/cockpit,mareklibra/cockpit,deryni/cockpit,stefwalter/cockpit,andreasn/cockpit,andreasn/cockpit,mvollmer/cockpit,martinpitt/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,andreasn/cockpit,garrett/cockpit,stefwalter/cockpit,deryni/cockpit,cockpituous/cockpit,andreasn/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,cockpit-project/cockpit,deryni/cockpit,garrett/cockpit,SotolitoLabs/cockpit,martinpitt/cockpit,deryni/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,moraleslazaro/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,cockpituous/cockpit