RemoveStringFromCSV: add unit test

Tested: only added a unit test and it passed.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: If68e47545f184b9fa22d701e78fb15b2b1b7949f
diff --git a/user_mgr.cpp b/user_mgr.cpp
index 7ee424d..b2047b2 100644
--- a/user_mgr.cpp
+++ b/user_mgr.cpp
@@ -148,7 +148,7 @@
                            });
 }
 
-static bool removeStringFromCSV(std::string& csvStr, const std::string& delStr)
+bool removeStringFromCSV(std::string& csvStr, const std::string& delStr)
 {
     std::string::size_type delStrPos = csvStr.find(delStr);
     if (delStrPos != std::string::npos)