Add InstancePCIRequests object

Part of blueprint pci-passthrough-sriov

Co-Authored-By: Dan Smith <dansmith@redhat.com>
Co-Authored-By: Baodong (Robert) Li <baoli@cisco.com>
Change-Id: I125e4afdf98a7073abcb8117bbb7a3e3fe2f9830
Merge "Add InstancePCIRequests object"