This resolves:

   https://bugzilla.redhat.com/show_bug.cgi?id=1045002

If a domain has an <interface type='hostdev'> or an <interface
type='network'> where the network itself is a pool of hostdev devices,
then libvirt will internally keep that device on both the interface
list *and* the hostdev list for the domain. One of the places this
comes in handy is when a new device is being added and libvirt wants
to find a unique "alias" name for it - it just scans through the
hostdev array and makes sure it picks a name that doesn't match the
alias of any device in that array.

However, when libvirtd was restarted, if there was an <interface
type='network'> with the network being a hostdev pool, the device
would not be added to the reconstructed internal hostdev array, so its
alias would not be found during a scan of the hostdev array, thus
attempts to add a new hostdev (or <interface type='hostdev'> or
<interface type='network'>) would result in a message like this:

internal error: unable to execute QEMU command 'device_add':
                Duplicate ID 'hostdev0' for device

This patch simply fixes the existing code in the domain XML parser
that fixes up the hostdev array in the case of <interface
type='hostdev'> to do the same thing in the case of <interface
type='network'> with a hostdev network.

This bug has existed since the very first addition of hostdev networks
to libvirt (0.10.0).