fix so copy failed error

Author: shockcao

mars/libraries/build_android.py

@@ -244,7 +244,8 @@ def main():
             SO_SYMBOL_CACHE_DIR = sdk_path + "/so_cache/symbol/"
             SO_DES_DIR = sdk_path + "/libs/"
             SO_SYMBOL_DES_IR = sdk_path + "/obj/local/"
-
+            if os.path.exists(SO_CACHE_DIR):
+                shutil.rmtree(SO_CACHE_DIR)
 
             for i in range(0, len(archs)):
                 print "build %s" %(archs[i])
@@ -283,7 +284,6 @@ def main():
             if "2" == num or "3" == num:
                 return
 
-
             if os.path.exists(SO_DES_DIR):
                 shutil.rmtree(SO_DES_DIR)
             if os.path.exists(SO_SYMBOL_DES_IR):