e temporarily a local OpenGL context

Change-Id: I086d826456d77bf978c3877ed6da92850878ad97
call glewInit in vcl's OpenGLContext just once

Change-Id: I9f9b50615e588e659c7fcdd016cf9ceb8407b974
improve the code for temporary OpenGl context

Change-Id: Ia66bf54539e67066a56bb50fb606e50e581bee73