Fix the terminate routine to avoid deadlock in ewk_shutdown

Fix the terminate routine to avoid deadlock in ewk_shutdown

If ewk_shutdown is called when renderer thread works,
the deadlock happens while exiting the web application.

In order to prevent this deadlock problem, crosswalk don't
terminate the web application directly, it terminate
the web application using ewk_view_page_close API.

By using ewk_view_page_close API, crosswalk can receive
the callback that renderer thread was terminated.
After then crosswalk call the ewk_shutdown.

Bug: http://suprem.sec.samsung.net/jira/browse/TSAM-11982

Change-Id: I0d6279be0a03835ab58e2bf21443dcbba286f823
Signed-off-by: Youngcheol Kang <ychul.kang@samsung.com>