Add support to use the field name in rdci

In the rdci dmon and fieldgroup, now the fields can be specified
using either number id or the field name.

When the rdc is async fetching metrics, it will not report that fetch
as an error.

Change-Id: I81331e2c239af987181147be5ac0e29ba1617ab4

rdci/include/RdciSubSystem.h

@@ -43,6 +43,8 @@ class RdciSubSystem {
      std::vector<std::string> split_string(const std::string& s,
             char delimiter) const;
      void show_common_usage() const;
+     bool get_field_id_from_name(const std::string& name,
+                uint32_t& value) const;  // NOLINT(runtime/references)
      rdc_handle_t rdc_handle_;
      std::string ip_port_;