XenAPI: Add the support for updating the status of the host.

  We added a function into the xenhost plugin to get information
about PCI devices. Roughly we run the lspci command on dom0. This
information will be used to get the list of pci devices  that are
passed on the pciback.hide dom0 command line.

  The hide option is used to hide the devices from the normal guest
drivers and assign them to the pciback kernel driver at boot on dom0
instead of their normal driver. We will parse the output of the lspci
command to find which device is using the pciback kernel driver and
thus to know if it has been passed to the pciback.hide option.

  This information will be used to perform the match with the
list of pci devices provided in pci_whitelist into /etc/nova/nova.conf.

Implements: blueprint pci-passthrough-xenapi

Change-Id: I465fc5d29f3c47ab0079adcfcc2d7d6501bd4b20
Merge "XenAPI: Add the support for updating the status of the host."