Store configuration file in repmgr.nodes table

When executing repmgr on remote nodes, we otherwise end up jumping
through hoops as we can't make assumptions about where the configuration
file is located, but really need to be able to provide it.

From a support point of view it will also make life easier as it will
be easy to specify exactly which file to provide.

configfile.h

@@ -13,6 +13,7 @@
 #define CONFIG_FILE_NAME	"repmgr.conf"
 #define MAXLINELENGTH		4096
 extern bool		config_file_found;
+extern char		config_file_path[MAXPGPATH];
 
 typedef enum {
 	FAILOVER_MANUAL,