Unify use of error codes across all exit statements

repmgr.h

@@ -47,11 +47,15 @@
 
 /* Exit return code */
 
+#define SUCCESS 0
 #define ERR_BAD_CONFIG 1
 #define ERR_BAD_RSYNC 2
 #define ERR_STOP_BACKUP 3
 #define ERR_NO_RESTART 4
 #define ERR_NEEDS_XLOG 5
+#define ERR_DB_CON 6
+#define ERR_DB_QUERY 7
+#define ERR_PROMOTED 8
 
 /* Run time options type */
 typedef struct {