Better error message on socket (#1477)

* checking errno

* improved socket error message

* improved message

* decode error code

* format

* clearer msg

* report write errors, handle SIGPIPE

* retry and cleaned up timeout

* removed read/write in DataSocket

slsSupportLib/include/sls/string_utils.h

@@ -64,4 +64,6 @@ bool replace_first(std::string *s, const std::string &substr,
 
 std::pair<std::string, uint16_t> ParseHostPort(const std::string &s);
 
+std::string to_lower(const std::string &s);
+
 } // namespace sls