libxl: fix cold plugged PCI devices with stubdomains

libxl: fix cold plugged PCI devices with stubdomains

Since 23565:72eafe80ebc1 the xenstore entries for the stubdomain's PCI were
never created and therefore the stubdom ends up waiting forever for the devices
which it has been asked to insert to show up.

Since the stubdomain is already running when we call the libxl_device_pci_add
loop in do_domain_create we should treat it as if "starting == 0".

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson.citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>