Support pure remote server for importing appliance

[julien-duponchelle]

Actually the import of appliance is mostly an operation of the gui taking advantage of direct access to the file system. But this doesn't work when your controller is remote.

Step to solve the issue:

• Pass to Image object in the gui the emulator type (qemu, iou...)
• And an endpoint for uploading images to a compute
• In the GUI use this endpoint instead of direct copy of the file
• Get the list of remote images and images in the Downloads directory in the appliance wizard
• Repare OVA support because we will break it as usual

Will solve #827

[julien-duponchelle]

The endpoint already exists we use it in the image manager

[julien-duponchelle]

I opened an issue about OVA support #1591 not sure that we really need to put effort on it. It's probably not use.

[julien-duponchelle]

Ok will be in alpha2