Enable trim_mode via '-' in ERB templates

This adds whitespace supression optionally, similar to the default
behavior in Rails ActionView ERB templates.

Just add - to a %> like so: -%> and it will remove trailing whitespace
and newlines. This can also be done to the beginning tag for removing
newlines from the beginning of the tag line.

lib/foreman/export/base.rb

@@ -119,7 +119,7 @@ private ######################################################################
   end
 
   def write_template(name, target, binding)
-    compiled = ERB.new(export_template(name)).result(binding)
+    compiled = ERB.new(export_template(name), nil, '-').result(binding)
     write_file target, compiled
   end