Description of problem:
Today we use custom templates created by unknown logic, based on several operating systems and configurations.

the flow to store,download and manage those templates is using custom code which is internal to lago and not using standard or known open source projects that already solved this problem like vagrant or virt-builder.

the purpose of this bug is to add a formal way of managing templates built as a plugin that will use virt-builder.
we choose virt-builder as the 1st plugin because its simplicity and the fact we can manage the templates on our own html server.

we might want to add in the future more plugins like glance or packager.io support.

the following might be opened as seperate bugs to handle each issue:

 - The plugin should support using images from libguestfs
 - The plugin should check if cloudinit is enabled and have ability to disable 
   it in the image, for performance purposes.
 - optional - check if artifactory can store images instead of http server, as 
     separate plugin?
 - check if its possible to provide support for legacy templates and new plugin at the same time, if not - we need to provide working version with legacy way and announce on new version without backward compatibility.



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