Directly clone tinyxml2

The build isn't happy with the Ubuntu package.

Change-Id: Id46b50b2f839005a46dd016f33931e32094ff721
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/build-unit-test-docker.sh b/build-unit-test-docker.sh
index 70dd201..ca45a8b 100755
--- a/build-unit-test-docker.sh
+++ b/build-unit-test-docker.sh
@@ -146,8 +146,7 @@
     lcov \
     libpam0g-dev \
     xxd \
-    wget \
-    libtinyxml2-6
+    wget
 
 RUN pip install inflection
 RUN pip install pycodestyle
@@ -244,6 +243,16 @@
 make -j$(nproc) && \
 make install
 
+# version from meta-openembedded/meta-oe/recipes-support/libtinyxml2/libtinyxml2_5.0.1.bb
+RUN curl -L -o tinyxml2.tar.gz https://github.com/leethomason/tinyxml2/archive/37bc3aca429f0164adf68c23444540b4a24b5778.tar.gz && \
+tar -xzf tinyxml2.tar.gz && \
+cd tinyxml2-3* && \
+mkdir build && \
+cd build && \
+cmake .. && \
+make -j$(nproc) && \
+make install
+
 RUN /bin/bash
 EOF
 )