httpsisoboot hook:
============
Let the VM boot from an ISO image made available via an https URL without
the need to import the ISO into an ISO storage domain.
The hook supports only the https protocols and the host should be able
to properly trust the provided URL.

The https source won't work reliably unless you can guarantee a low latency
between the VM and the web server: in case of latency spikes or packet loss,
the guest will see EIO errors.
So it could be adopted with a local web server with plenty of spare capacity
and a fast LAN link to the oVirt nodes, but using it with remotely available
ISO images is not recommended.

The support for plain http has been removed from qemu-kvm-rhev and qemu-kvm-ev
 as a security improvement but it's available upstream.

syntax:
    httpsisoboot=https://server/path/to/disk.iso


The hook will create an additional CDROM device from the provided URL.
It will also increase all other boot order values to use it as the
first boot option.
For ex:
    <disk type='network' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source protocol="https" name="/path/to/disk.iso">
        <host name="server" port="8080"/>
      </source>
      <target dev='hdc' bus='ide' tray='closed'/>
      <readonly/>
      <boot order='1'/>
    </disk>

Installation:
1. Define a new custom VM property
* Use engine-config to set the appropriate custom properties as such:
    # engine-config -s UserDefinedVMProperties='httpsisoboot=^https:\/\/.*$'

* Setting UserDefinedVMProperties overwrites all previous custom properties.
  If you've already defined other custom properties, you may wish to append instead:
    sudo engine-config -g UserDefinedVMProperties
  Copy the value into $PREVIOUS_PROPERTIES, then use:
    # engine-config -s UserDefinedVMProperties='$PREVIOUS_PROPERTIES;httpsisoboot=^https:\/\/.*$'

* Verify that the httpsisoboot custom property was properly added:
    # engine-config -g UserDefinedVMProperties

2. In order that your changes will take effect you need to restart the ovirt engine:
    # systemctl restart ovirt-engine

Usage:
Being a boot option, you probably prefer "Run Once" dialog which mean that
you add the custom property to the VM only this time, next time that you run
the VM it will run without the custom property that you just provided.
The "Run Once" dialog can be found in the VMs tab at the drop down menu beside
the green "Play" button (after the "Clone VM" button).
Select the last option from the list with the label "Custom Properties"
and expand it. Add your httpsisoboot property and configure its value to
the required URL.