Add libi2c-dev to image

As i2c-dev-user.h was removed from Yocto, Entity-Manager
and some other packages are no longer carrying this header
and using the supported smbus.h and i2c-dev.h. Add these
files to the CI so that they don't have to carry copies.

Tested-by: Built review 13490 successfully

Change-Id: I45f1d3421fed2b5a512540d2414c2ab9de998f77
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/build-unit-test-docker.sh b/build-unit-test-docker.sh
index fac4c97..499c17c 100755
--- a/build-unit-test-docker.sh
+++ b/build-unit-test-docker.sh
@@ -146,6 +146,7 @@
     lcov \
     libpam0g-dev \
     xxd \
+    libi2c-dev \
     wget
 
 RUN pip install inflection