build-unit-test-docker: Only build phosphor-logging library

We don't need the server or any of the tests.

Change-Id: I0509fbcbaa6486027902a8e6bbc43f637f4a3935
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index b0b4a8b..c81f965 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -196,6 +196,8 @@
         ],
         build_type="meson",
         config_flags=[
+            "-Dlibonly=true",
+            "-Dtests=disabled",
             f"-Dyamldir={prefix}/share/phosphor-dbus-yaml/yaml",
         ],
     ),