Nova bugfix 1805969

[darmach]

Fix for nova not parsing RequestSpec.pci_request when resizing.

Quoting upstream change:

Nova uses the RequestSpec.pci_request in the PciPassthroughFilter to
decide if the PCI devicesm, requested via the pci_alias in the flavor
extra_spec, are available on a potential target host. During resize the
new flavor might contain different pci_alias request than the old flavor
of the instance. In this case Nova should use the pci_alias from the new
flavor to scheduler the destination host of the resize. However this
logic was missing and Nova used the old pci_request value based on the
old flavor. This patch adds the missing logic.

This behaviour resulted in resize not being executed.