scroller: fix to skip focus for unfocusable scroller

scroller: fix to skip focus for unfocusable scroller

this commit is merged from upstream(D4056)

Summary:
There is a issue about passing the focus to unfocusable scroller.
To prevent the issue, check the status of focusable object and child
object
before passing the focus.

Test Plan:
{F38439}

I changed the test file.
The problem occured as below.

1. click button
2. show popup
3. click cancel button in popup
4. lost the focus

Reviewers: Hermet, raster, cedric
Reviewed By: cedric
Subscribers: minkyu, sju27, cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D4056

Change-Id: I66ebde6ed5f01ca8b54fe9cd556f4745dd89db8a
Signed-off-by: Wonki Kim <wonki_.kim@samsung.com>