Store persisted config directory

The persisted configuration subdirectory will be used to store changes to
the configuration. The gwdirs.h header now supports setting and getting
the value for this directory.

server/core/config.c

@@ -65,6 +65,7 @@
 #include <maxscale/service.h>
 #include <maxscale/spinlock.h>
 #include <maxscale/utils.h>
+#include <maxscale/gwdirs.h>
 
 typedef struct duplicate_context
 {

server/core/gwdirs.c

@@ -26,6 +26,17 @@ void set_configdir(char* str)
     configdir = str;
 }
 
+/**
+ * Set the configuration parts file directory
+ * @param str Path to directory
+ */
+void set_config_persistdir(char* str)
+{
+    MXS_FREE(config_persistdir);
+    clean_up_pathname(str);
+    config_persistdir = str;
+}
+
 /**
  * Set the log file directory
  * @param str Path to directory
@@ -160,6 +171,15 @@ char* get_configdir()
     return configdir ? configdir : (char*) default_configdir;
 }
 
+/**
+ * Get the configuration file directory
+ * @return The path to the configuration file directory
+ */
+char* get_config_persistdir()
+{
+    return config_persistdir ? config_persistdir : (char*) default_config_persistdir;
+}
+
 /**
  * Get the PID file directory which contains maxscale.pid
  * @return Path to the PID file directory