build-qemu-robot-docker.sh: add rust to package

The latest cryptography packages require rust

Change-Id: I71a1210ece3a151e978c2d934a1899d6effbe039
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/scripts/build-qemu-robot-docker.sh b/scripts/build-qemu-robot-docker.sh
index f00b996..956f34b 100755
--- a/scripts/build-qemu-robot-docker.sh
+++ b/scripts/build-qemu-robot-docker.sh
@@ -98,7 +98,8 @@
     libxslt-dev \
     python3-pip \
     ipmitool \
-    xvfb
+    xvfb \
+    rustc
 
 RUN apt-get update -qqy \
   && apt-get -qqy --no-install-recommends install firefox \