Pass RUST_BACKTRACE when running docker.

Author: jfgoog

src/ci/docker/run.sh

@@ -205,7 +205,7 @@ mkdir -p $objdir/tmp
 mkdir -p $objdir/cores
 mkdir -p /tmp/toolstate
 
-args=
+args=" --env RUST_BACKTRACE"
 if [ "$SCCACHE_BUCKET" != "" ]; then
     args="$args --env SCCACHE_BUCKET"
     args="$args --env SCCACHE_REGION"