Clean up calls to repmgr_atoi()

In some places we were still providing "false" from the original implementation,
which was intended to indicate whether a negative value was allowed.

This has not been a problem, as it merely means we have been providing "0",
which is the same thing; however we can finer-tune some of the calls
(e.g. node ID must be or greater).

repmgr.h

@@ -58,7 +58,7 @@
 #define NODE_NOT_FOUND		-1
 #define NO_UPSTREAM_NODE	-1
 #define UNKNOWN_NODE_ID		-1
-
+#define MIN_NODE_ID          1
 #define VOTING_TERM_NOT_SET -1
 
 #define BDR2_REPLICATION_SET_NAME "repmgr"