CA-115915: Network backend is not a VIF thing

It's a host thing, or at least, a PIF thing. But certainly not
a VIF thing!

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Use syslog from xcp

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
CA-114673: Default create-time for a domain is 'now' not 0

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>

Description of the problem from John Else:

The events within xenopsd happen in approximately this order
(n.b. the sender and receiver are different threads in the
same xenopsd, as this is a localhost migration):

 1   Sender makes a request to receiver's receive_memory handler
 2   Receiver creates a new domain into which it will receive
     the memory (including writing the new domain's tree under
     /vm/<uuid>/<domid>)
 3   Sender initiates a save pointing at the fd used by the
     request from step 1
 4   Receiver initiates a restore using the other end of the
     above fd

Problem is, step 3 needs to know which of the two domains to
save, and there's no guarantee that step 3 starts after step 2
is finished. If the xenstore tree hasn't been written yet,
xenopsd defaults to reading the new domain's creation time as
zero, so will always choose it as the old domain to be saved.
Use singleton usbdevice_list instead of usbdevice

This is a workaround since the default value of [] for usbdevice_list is
interpreted as a specified option in libxl and libxl disallows specifying both
the usbdevice and usbdevice_list options.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Don't exit when encountering exception from Domain.create_new

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Only export VNC over Unix sockets for upstream qemu

This special cases the change made by 4ca23dbe52a26e377131b626049fc4104c998530.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #21 from simonjbeaumont/cp-6238

Fix HVM domain creation using libxl