Set the scenario/img_dir option for tempest.conf

The default value does not work unless devstack is installed in
/opt/stack/new/devstack. This patch changes the img_dir option to point
to the correct install location.

Change-Id: Iea41d209dad10b2f9a7c97efd55c39a8d29347cc
xenapi: cleanup VM Installation

VM installation created a machine with multiple network interfaces. This
is a needless complexity at that point, we only need one interface. This
change removes the complex network interface setup from
install-os-vpx.sh script, so that only one network interface is created,
which is connected to the selected network (management by default). This
change also removes a lot of non-used code from install-os-vpx.sh
Specify the network to be used for ubuntu netinstall with:

    UBUNTU_INST_BRIDGE_OR_NET_NAME

defaults to $MGT_BRIDGE_OR_NET_NAME.

This change also includes:
 - use precise as default

Related to blueprint xenapi-devstack-cleanup

Change-Id: Ib0a0a316e849f2c2651305ea657c84820cd2bb3b
Start using cinder rest api v2 by default

It's ready, it's time. Has deprecation support for v1 parameters as
well.

Change-Id: I19168d55c2ffad2b1cd668b6c1341dc8e49e9c1f