unit-test: Make sure tests build

Some of our packages now support an option for explicitly enabling test
cases to build. This ensures for their autotools configure run that they
have all of the needed dependencies for running the test cases. Since it
is important for the CI unit-test script to run and configure the tests
properly, pass this flag.

Change-Id: I65363d92aa7b35530a1ef5e1059cb100428ac5f0
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/scripts/unit-test.py b/scripts/unit-test.py
index 1642ade..ae02d59 100755
--- a/scripts/unit-test.py
+++ b/scripts/unit-test.py
@@ -286,6 +286,7 @@
         # Build & install this package
         conf_flags = [
             '--disable-silent-rules',
+            '--enable-tests',
             '--enable-code-coverage',
             '--enable-valgrind',
         ]