media-libs/gst-plugins-base-1.14: skip opengl tests, fix the rest to pass

media-libs/gst-plugins-base-1.14: skip opengl tests, fix the rest to pass

OpenGL tests fail with EGL init trouble, like they did in gst-plugins-bad
(if the whole testsuite wouldn't be restricted), so disable the opengl tests
for now. Ideally we'd get them to work without skipping, but that's a battle
for a much much rainier day.
Other failures happening on my machine were caused by GSETTINGS_BACKEND=dconf
export from env.d due to having dconf installed, so unset it to use memory
backend by GSettings.
Apparently there were more test failures under some conditions for 1.12, but
I couldn't reproduce those in 1.14, and probably not with 1.12 either. Those
will need to be rechecked by people having the failures or new +1's.

Package-Manager: Portage-2.3.40, Repoman-2.3.9