Makefile+action: add make unit-module to test submodules

This commit adds a new command `make unit-module` to run unit tests for
submodules to avoid future build errors.

scripts/unit_test_modules.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+IGNORE="tools"
+SUBMODULES=$(find . -mindepth 2 -name "go.mod" | cut -d'/' -f2 | grep -v "$IGNORE")
+
+for submodule in $SUBMODULES
+do
+  pushd $submodule
+
+  echo "Running submodule unit tests in $(pwd)"
+  echo "testing $submodule..."
+  go test -timeout=5m || exit 1
+  
+  if [[ "$submodule" == "kvdb" ]]
+  then
+      echo "testing $submodule with sqlite..."
+      go test -tags="kvdb_sqlite" -timeout=5m || exit 1
+      
+      echo "testing $submodule with postgres..."
+      go test -tags="kvdb_postgres" -timeout=5m || exit 1
+      
+      echo "testing $submodule with etcd..."
+      go test -tags="kvdb_etcd" -timeout=5m || exit 1
+  fi
+  
+  popd
+done