package_tool: fix calculate checksum to consider only files

Change-Id: I7676fbb51fb3d4f3f4ad174241c0e93418a8c49f
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/osmclient/common/package_tool.py b/osmclient/common/package_tool.py
index 203806e..3da96d5 100644
--- a/osmclient/common/package_tool.py
+++ b/osmclient/common/package_tool.py
@@ -150,7 +150,7 @@
             :returns: None
         """
         self._logger.debug("")
-        files = [f for f in glob.glob(package_folder + "/**/*.*", recursive=True)]
+        files = [f for f in glob.glob(package_folder + "/**/*.*", recursive=True) if os.path.isfile(f)]
         with open("{}/checksums.txt".format(package_folder), "w+") as checksum:
             for file_item in files:
                 if "checksums.txt" in file_item: