Add NGRAPH_INTRA_OP_PARALLELISM to control size of thread pools. (#1248)

* Add NGRAPH_INTRA_OP_PARALLELISM to control size of thread pools.

* Initialize variable.

src/ngraph/runtime/cpu/kernel/eigen_thread_pool.cpp

@@ -29,12 +29,19 @@ namespace ngraph
                 static int GetNumCores()
                 {
                     const auto omp_num_threads = std::getenv("OMP_NUM_THREADS");
-                    int count;
+                    const auto ngraph_intra_op_parallelism =
+                        std::getenv("NGRAPH_INTRA_OP_PARALLELISM");
+                    int count = 0;
 
                     if (omp_num_threads && (count = std::atoi(omp_num_threads)))
                     {
                         return count;
                     }
+                    else if (ngraph_intra_op_parallelism &&
+                             (count == std::atoi(ngraph_intra_op_parallelism)))
+                    {
+                        return count;
+                    }
                     else
                     {
                         count = std::thread::hardware_concurrency() >> 1;