elm_panel: make "panel scrollable" work in elementary_test
elm_panel: make "panel scrollable" work in elementary_test

Summary:
Thumbscroll is disabled in default configuration,
but "scrollable" feature in panel only works when thumbscroll is turned on.
To make "scrollable" work always in elementary test,
this patch enables thumbscroll temporarily regardless of configuration.
(configuration is restored when sample window is closed.)

Reviewers: Hermet, seoz

Subscribers: seoz, Hermet

Differential Revision: https://phab.enlightenment.org/D1983

rvandegrift/elementary,FlorentRevest/Elementary,tasn/elementary,tasn/elementary,tasn/elementary,rvandegrift/elementary,rvandegrift/elementary,tasn/elementary,tasn/elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,rvandegrift/elementary