allow the MAKEJOBS environment variable to specified for docker, too

docker-build.sh

@@ -27,6 +27,8 @@ docker run -ti -h ffpb-build -v "$MYDIR:/code" \
     --env BUILD_TS="$BUILD_TS" \
     --env BASE="$BASE" \
     --env BRANCH="$BRANCH" \
+    --env BROKEN="$BROKEN" \
+    --env MAKEJOBS="$MAKEJOBS" \
     --env VERBOSE="$VERBOSE" \
     --env VERSION="$VERSION" \
     --env TARGETS="$TARGETS" \