If --dry-run specified, ensure minimum log level is INFO

When executed with --dry-run, repmgr outputs detail about what would
happen using log level INFO. If the log_level is configured to
NOTICE or higher, it's possible some or all of the --dry-run output
might not be displayed.

Addresses GitHub #441.

log.h

@@ -128,6 +128,7 @@ bool		logger_shutdown(void);
 
 void		logger_set_verbose(void);
 void		logger_set_terse(void);
+void		logger_set_min_level(int min_log_level);
 
 void
 log_detail(const char *fmt,...)