* one_vm: fix syntax error when creating VMs with a more complex template
with more complex templates that make use of quoted strings the new
"render" method fails to produce a template that is accepted by
OpenNebula. ==> escape double quotes in strings to make OpenNebula
happy again.
I also tested whether newlines need to be escaped, looks like they are
fine as they are.
Fixes#6225
* module_utils/opennebula: skip empty values in render
