Update of VPP_STABLE_VER and DPDK_STABLE_VER files

- use new vpp ref build - ubuntu 16.04:
  18.10-rc0~422-geeadc14~b5124

- use new vpp ref build - centos7:
  18.10-rc0~424_gef90ed0~b5050

- use new dpdk version:
  18.08-vpp3

NOTE: Centos7 and Ubuntu16.04 builds are litle bit different
      because of availability of builds on repo.

Change-Id: I6cefd91351848fb075935ae9b41354d3432eacf3
Signed-off-by: Jan Gelety <jgelety@cisco.com>