This PR add KVM support in the appliance schema.
It's a part of https://github.com/GNS3/gns3-gui/issues/904 from
@boenrobot
KVM has three value:
* "require" - Forbid installation on the target server if KVM is not
available there (i.e. a Windows and OSX; be it local or remote). Install
only with KVM enabled.
* "allow" - Enable KVM if supported on the target server, but allow
installation to continue with KVM disabled if not supported (this should
be the default).
* "disable" - Even if KVM is supported on the target server, install with
KVM disabled.
All appliances have been updated to reflect their correct value.
Also it's add a sample tool for quickly patch all appliances.
