bitbake: adding a new comment should be placed on a new line

In this case, the comment is appended to the end of the file.
Some text editors, do not place  a '\n' to the end of the file
after saving it.

[YOCTO #4636]
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bitbake: python funcname can not include special character @

[YOCTO #4772]

When path:file change to python function, it maybe include '@' character.
So, add the special character to change to '_' for avoid error.

Signed-off-by: Li Wang <li.wang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>