one_vm: fix syntax error when creating VMs with a more complex template (#6294)

* 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

plugins/module_utils/opennebula.py

@@ -45,6 +45,8 @@ def render(to_render):
     """Converts dictionary to OpenNebula template."""
     def recurse(to_render):
         for key, value in sorted(to_render.items()):
+            if value is None:
+                continue
             if isinstance(value, dict):
                 yield '{0:}=[{1:}]'.format(key, ','.join(recurse(value)))
                 continue
@@ -52,6 +54,9 @@ def render(to_render):
                 for item in value:
                     yield '{0:}=[{1:}]'.format(key, ','.join(recurse(item)))
                 continue
+            if isinstance(value, str):
+                yield '{0:}="{1:}"'.format(key, value.replace('\\', '\\\\').replace('"', '\\"'))
+                continue
             yield '{0:}="{1:}"'.format(key, value)
     return '\n'.join(recurse(to_render))