gst-libs: use GST_*_1_0 environment variables everywhere

gst-libs: use GST_*_1_0 environment variables everywhere

The _1_0 suffixed environment variables override the
non-suffixed ones, so if we're in an environment that
sets the _1_0 suffixed ones, such as jhbuild, we need
to set those to make sure ours actually always get
used.