If multiple DRM connectors are connected, currently the first one is
picked. Improve this by adding an environment variable that allows for
choosing a connector by name. The connector name has been made so they
are compatible with modetest/modeprint DRM utilities.
Related to #490
* List all connectors, modes, and encoders, even after picking one
* Add missing DRM_MODE_CONNECTOR_DPI string for logging and improve
existing strings
* Make sure the names matches modetest/modeprint from DRM utilities
Related to #490
This adds a few missing gst_object_unref calls for the opengl context in
gstglwindow_gbm_egl.c, as well as the missing close call for the
drm node fd in gst_gl_display_gbm_finalize.