Merge branch 'ca-171870' into 'master'

CA-171870: vpx upgrade from centos5 to centos7

New VPX PV console write does not work now because new VPX is a HVM guest, we add sshd into new VPX guest, do self configuration through ssh.

We add a flag VPX_OS_VERSION in sequence file to distinguish the old VPX and new VPX. If VPX_OS_VERSION equals to CentOS7, then we use the new XenRT code to test. Otherwise (VPX_OS_VERSION is CentOS 5 or missing), then we use the old XenRT code to test.

Both of the old VPX and new VPX XenRT test have been verified.

See merge request !13

diff --cc exec/xenrt/lib/xenserver/guest.py
Simple merge

diff --cc exec/xenrt/objects.py
Simple merge