Setting ELM_ENGINE Environment value.

Setting ELM_ENGINE Environment value.

There is gl engine issue in latest Tizen 2.4 platform binary.
In order to solve this problem, it is needed to set ELM_ENGINE
environment value as gl.
This patch apply this setting in mini_browser code level.
When gl issue is solved in Tizen 2.4 platform,
This patch should be reverted.

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=10787
Reviewed by: Piotr Tworek, Youngbok Yoon, joonhwan kwon

Change-Id: I5d6695502ff7d7be39e00293be1b236b15ec4314
Signed-off-by: Jongsoo Yoon <join.yoon@samsung.com>