Enable destruction of servers

The servers can now be destroyed which removes them from the list of
active servers. If the server was not created at runtime, a warning is
logged.

include/maxscale/monitor.h

@@ -233,4 +233,11 @@ connect_result_t mon_connect_to_db(MONITOR* mon, MONITOR_SERVERS *database);
 void mon_log_connect_error(MONITOR_SERVERS* database, connect_result_t rval);
 void mon_log_state_change(MONITOR_SERVERS *ptr);
 
+/**
+ * Check if a monitor uses @c servers
+ * @param server Server that is queried
+ * @return True if server is used by at least one monitor
+ */
+bool monitor_server_in_use(const SERVER *server);
+
 MXS_END_DECLS

include/maxscale/server.h

@@ -243,4 +243,13 @@ extern void server_update_ssl(SERVER *server, const char *key, const char *value
  */
 bool server_serialize(SERVER *server);
 
+/**
+ * @brief Destroy a server
+ *
+ * This removes any created server configuration files and marks the server removed
+ * If the server is not in use.
+ * @param server Server to destroy
+ */
+void server_destroy(SERVER *server);
+
 MXS_END_DECLS

include/maxscale/service.h

@@ -257,4 +257,11 @@ static inline uint64_t service_get_capabilities(const SERVICE *service)
     return service->capabilities;
 }
 
+/**
+ * Check if a service uses @c servers
+ * @param server Server that is queried
+ * @return True if server is used by at least one service
+ */
+bool service_server_in_use(const SERVER *server);
+
 MXS_END_DECLS