elm_scroller: keep contents layout rel even if rtl is set

elm_scroller: keep contents layout rel even if rtl is set

Summary:
Once rtl mode is set, elm_layout reverses its x-axis.
however, scroller uses elm_layout to contain both original content and
proxy image of it when loop mode is set.

In this situation, elm_layout should not reverse its x-axis when It is
used for container of proxy to support loop mode of scroller.

This commit will not apply rtl mode to contents layout (mirrored set)

Test Plan:
* Check that there is a proxy image over right edge of original content.

1. Run elementary_test
2. Open scroller
3. Switch UI_mirrored mode on
4. Test (Control with keyboard / mouse wheel control looks bad on rtl mod)
   a. go to the right edge with keyboard
   b. get over the edge

Reviewers: woohyun, z-wony, jpeg, cedric

Differential Revision: https://phab.enlightenment.org/D4568

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>