[UnitTest] Reset shared-pointer explicitly in MklDnnFunctionalTest (#5543)

inference-engine/tests_deprecated/functional/shared_tests/io_blob_tests/dims_tests.hpp

@@ -49,6 +49,7 @@ protected:
     }
 
     void TearDown() override {
+        PluginCache::get().reset();
     }
 
     std::string ConvNet(const int batch, TBlob<uint8_t>::Ptr &weights) {

inference-engine/tests_deprecated/functional/shared_tests/io_blob_tests/layout_tests.hpp

@@ -139,6 +139,7 @@ protected:
     }
 
     void TearDown() override {
+        PluginCache::get().reset();
     }
 
     template <Precision::ePrecision PRC>