Add useful helper functions for tests

Trying to reduce code duplication by putting common
EGL functions used by opengl and surfaceflinger tests
here.
Test: adb shell /data/nativetest/test-opengl-gl2_basic/test-opengl-gl2_basic

Merged-In: Id7a32aedc565f3fbe56fa62ceb79cbb1e8c80727
Change-Id: Id7a32aedc565f3fbe56fa62ceb79cbb1e8c80727
(cherry picked from commit fe98f50b)