Utils: add IsDotOrDotDot() and use it in the appropriate places

Change-Id: I704522b26acfb3e7c423d9a14d69ede513b50482
diff --git a/Utils.h b/Utils.h
index 5351450..27889c6 100644
--- a/Utils.h
+++ b/Utils.h
@@ -168,6 +168,8 @@
 status_t UnmountTreeWithPrefix(const std::string& prefix);
 status_t UnmountTree(const std::string& mountPoint);
 
+bool IsDotOrDotDot(const struct dirent& ent);
+
 status_t DeleteDirContentsAndDir(const std::string& pathname);
 status_t DeleteDirContents(const std::string& pathname);