Split cpu_fusion.cpp into cpu_fusion.cpp and cpu_test.cpp; clean up headers (#748)

*  split cpu_fusion into cpu_fusion and cpu_test; clean up headers

* fix formatting

* add new line to tensor_mask.hpp

test/CMakeLists.txt

@@ -79,7 +79,7 @@ endif()
 if(NGRAPH_CPU_ENABLE AND LLVM_INCLUDE_DIR)
     include_directories(SYSTEM ${LLVM_INCLUDE_DIR})
     link_directories(${LLVM_LIB_DIR})
-    set(SRC ${SRC} backend_performance.cpp codegen.cpp cpu_fusion.cpp)
+    set(SRC ${SRC} backend_performance.cpp codegen.cpp cpu_fusion.cpp cpu_test.cpp)
     set(BACKEND_NAMES ${BACKEND_NAMES} "CPU")
 endif()