Introduce new domain create APIs to pass pre-opened FDs to LXC

With container based virt, it is useful to be able to pass
pre-opened file descriptors to the container init process.
This allows for containers to be auto-activated from incoming
socket connections, passing the active socket into the container.

To do this, introduce a pair of new APIs, virDomainCreateXMLWithFiles
and virDomainCreateWithFiles, which accept an array of file
descriptors. For the LXC driver, UNIX file descriptor passing
will be used to send them to libvirtd, which will them pass
them down to libvirt_lxc, which will then pass them to the container
init process.

This will only be implemented for LXC right now, but the design
is generic enough it could work with other hypervisors, hence
I suggest adding this to libvirt.so, rather than libvirt-lxc.so

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

libvirt-override-virConnect.py

@@ -310,3 +310,33 @@
         if ret == -1:
             raise libvirtError ('virConnectRegisterCloseCallback() failed', conn=self)
         return ret
+
+    def createXMLWithFiles(self, xmlDesc, files, flags=0):
+        """Launch a new guest domain, based on an XML description similar
+        to the one returned by virDomainGetXMLDesc()
+        This function may require privileged access to the hypervisor.
+        The domain is not persistent, so its definition will disappear when it
+        is destroyed, or if the host is restarted (see virDomainDefineXML() to
+        define persistent domains).
+
+        @files provides an array of file descriptors which will be
+        made available to the 'init' process of the guest. The file
+        handles exposed to the guest will be renumbered to start
+        from 3 (ie immediately following stderr). This is only
+        supported for guests which use container based virtualization
+        technology.
+
+        If the VIR_DOMAIN_START_PAUSED flag is set, the guest domain
+        will be started, but its CPUs will remain paused. The CPUs
+        can later be manually started using virDomainResume.
+
+        If the VIR_DOMAIN_START_AUTODESTROY flag is set, the guest
+        domain will be automatically destroyed when the virConnectPtr
+        object is finally released. This will also happen if the
+        client application crashes / loses its connection to the
+        libvirtd daemon. Any domains marked for auto destroy will
+        block attempts at migration, save-to-file, or snapshots. """
+        ret = libvirtmod.virDomainCreateXMLWithFiles(self._o, xmlDesc, files, flags)
+        if ret is None:raise libvirtError('virDomainCreateXMLWithFiles() failed', conn=self)
+        __tmp = virDomain(self,_obj=ret)
+        return __tmp