unit-test: Output googletest binaries with debugging info

A previous change b1da12722a7a8e8cb95be004e0f0aa4b22094001, added
debug symbols for dev versions of installed packages inside the unit test
container. Since googletest is also a development dependency and is
often involved in the debugging process, make sure it produces the
debugging symbols inside of its binaries.

Change-Id: I2469dab3a88c2e786eea1eb4126dde2a8a38ef79
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/build-unit-test-docker.sh b/build-unit-test-docker.sh
index ef3045c..680ce2d 100755
--- a/build-unit-test-docker.sh
+++ b/build-unit-test-docker.sh
@@ -115,7 +115,7 @@
 RUN wget -O googletest.tar.gz https://github.com/google/googletest/archive/ba96d0b1161f540656efdaed035b3c062b60e006.tar.gz
 RUN tar -xzf googletest.tar.gz
 RUN cd googletest-* && \
-cmake -DBUILD_GTEST=ON -DBUILD_GMOCK=ON -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=ON -DCMAKE_INSTALL_PREFIX:PATH=/usr . && \
+cmake -DBUILD_GTEST=ON -DBUILD_GMOCK=ON -DCMAKE_BUILD_TYPE=RelWithDebInfo -DBUILD_SHARED_LIBS=ON -DCMAKE_INSTALL_PREFIX:PATH=/usr . && \
 make && make install
 
 RUN wget https://github.com/USCiLab/cereal/archive/v1.2.2.tar.gz