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

include/rdc_lib/impl/RdcMetricFetcherImpl.h

@@ -60,7 +60,9 @@ class RdcMetricFetcherImpl: public RdcMetricFetcher {
     uint64_t now();
     void get_ecc_error(uint32_t gpu_index,
         uint32_t field_id, rdc_field_value* value);
-    void async_get_pcie_throughput(uint32_t gpu_index,
+
+    //!< return true if starting async_get
+    bool async_get_pcie_throughput(uint32_t gpu_index,
         uint32_t field_id, rdc_field_value* value);
     void get_pcie_throughput(const RdcFieldKey& key);