install_pip script fails if pip was not installed

'set -o errexit' recently added to the pip installer script, which causes
the script fail when it does not able to find an already installed pip.

This change handles the situation when pip is not installed.

Change-Id: I18a42d13c4be6699db21ec5b6a095a88a199912d
XenAPI: Get the management network dynamically

xenbr0 is correct for most installations, but not all.  Notable xenserver-core
may use a differently named device.  Since we can auto detect this, remove the
config and do so.

Change-Id: I989f6ddd5ffb526ab350f263ef6fc402c596304a
XenServer hypervisor plugin

Convert XenServer hypervisor configuration in Nova to the new plugin setup.

Change-Id: I8916560ca3f2dae8b8d8bcb60b7aa2eb5984cbcb
Use the rdo havana repo with the RHEL family

In devstack viewpoint there is not too much differences at the moment.
But using the grizzly named repo close to havana release, was strange to me.

Switching to the repo link which does not have a version like '-3'.

Change-Id: Ib421d50d19baeeeff264aa0cb9c105fffcf572f8
Added Savanna Project

Added services Savanna, Savanna Dashboard, Savanna python client.

Implements blueprint devstack-savanna-support
Implements blueprint devstack-integration

Change-Id: I8725f59a0cc9aef4817988470313136c56711cf1