Add tinyxml2 dependency

Change-Id: If1f180145ed87c283c7248589ac1e9a1690aacfc
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/build-unit-test-docker.sh b/build-unit-test-docker.sh
index 56ebae9..22e54e6 100755
--- a/build-unit-test-docker.sh
+++ b/build-unit-test-docker.sh
@@ -117,7 +117,8 @@
     lcov \
     libpam0g-dev \
     xxd \
-    wget
+    wget \
+    tinyxml2
 
 RUN pip install inflection
 RUN pip install pycodestyle