Keep only the minimum text for multiline comments

Previously, the following code:

    -#
      One line

      Two line

    %notice-multiple-spaces

...would have resulted in comment text with extra trailing lines:

   "\nOne line\nTwo line\n\n"

This was because we were including lines up to the successor node.
Strip trailing whitespace to fix it.

Change-Id: Ia87922275c1a8387be0a69faea8bce7bdfe06a4a
Reviewed-on: http://gerrit.causes.com/44992
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>