Unify all error report to ereport in cdbutil.c:getCdbComponentInfo. (#5802)

* Unify all error report to ereport in cdbutil.c:getCdbComponentInfo.

* Change the message to lower case which is the usual PostgreSQL
style for error messages.

src/backend/cdb/cdbutil.c

@@ -266,7 +266,9 @@ getCdbComponentInfo(bool DNSLookupAsError)
 		 */
 		if (pRow->hostaddrs[0] == NULL &&
 			pRow->role == GP_SEGMENT_CONFIGURATION_ROLE_PRIMARY)
-			elog(DNSLookupAsError ? ERROR : LOG, "Cannot resolve network address for dbid=%d", dbid);
+			ereport(DNSLookupAsError ? ERROR : LOG,
+					(errcode(ERRCODE_CONNECTION_FAILURE),
+					errmsg("cannot resolve network address for dbid=%d", dbid)));
 
 		if (pRow->hostaddrs[0] != NULL)
 			pRow->hostip = pstrdup(pRow->hostaddrs[0]);

src/test/isolation2/expected/fts_dns_error.out

@@ -110,7 +110,7 @@ t
 
 -- wait until fts done the probe and this query will fail
 0<:  <... completed>
-ERROR:  Cannot resolve network address for dbid=2 (cdbutil.c:269)
+ERROR:  cannot resolve network address for dbid=2
 
 -- verify a fts failover happens
 select count(*) from gp_segment_configuration where status = 'd';