tests: test_egl should destroy the EglImageKHR it creates

test_egl creates an EglImageKHR but never destroys it so the EGL
drivers might be holding on to the native buffer even after test_egl
releases it.

Signed-off-by: Kalle Vahlman <kalle.vahlman@movial.com>
Merge pull request #148 from kvahlman/cleanup-in-test_egl

tests: test_egl should destroy the EglImageKHR it creates