xenapi: preinstall python netaddr

On our CI system, the devstack instance was reporting errors, that are
related to devstack's address_in_net function - that requires the python
netaddr library to be installed. This patch preinstalls this python
package.

Fixes bug 1097667

Change-Id: I8af199427f06cfdf0a68d96d87fe3e541199dca7

tools/xen/prepare_guest.sh

@@ -22,7 +22,7 @@ STACK_USER="$3"
 # Install basics
 apt-get update
 apt-get install -y cracklib-runtime curl wget ssh openssh-server tcpdump ethtool
-apt-get install -y curl wget ssh openssh-server python-pip git vim-nox sudo
+apt-get install -y curl wget ssh openssh-server python-pip git vim-nox sudo python-netaddr
 pip install xenapi
 
 # Install XenServer guest utilities