Update of VPP_STABLE_VER files

- use new vpp ref build - ubuntu 16.04:
  17.10-rc0~263-gedfa2fd~b2799_amd64

- use new vpp ref build - centos7:
  17.10-rc0~263_gedfa2fd~b2796.x86_64

- builds tested by semiweekly jobs:
  https://jenkins.fd.io/view/csit/job/csit-vpp-verify-master-ubuntu1604-semiweekly/69/
  https://jenkins.fd.io/view/csit/job/csit-vpp-verify-master-centos7-semiweekly/69/

Change-Id: I510d288a4a5444f980769d7fd13ab1ff46d227a5
Signed-off-by: Jan Gelety <jgelety@cisco.com>