Fix convert_node_to_xenserver.sh

After a1f2a62ba994d8857122329b4bd037b0924f7bd6 the conversion scripts
not worked, because the bootmenu's entry became `xe` instead of
`xe-serial`. It broke the whole conversion. This fix adopts to that
change, and expects `xe` as the menu label.
Move static definition of forwarding.conf later in script

this is the equivalent of https://review.openstack.org/#/c/123785/
Add timestamps to prepare_node_devstack.sh
Use updated trusty image

The main difference is that 1.1.4 is a `dist-upgrade` -ed trusty image
with a new kernel 3.13.0-36 and that should fix the jdk related issues
that resulted in strange log entries in dmesg and also making the system
unstable.