[4281] Addressed further review comments.

- Always invoke mysql_insert_id to retrieve host_id value
- exit if connection with  MySql database is lost

src/lib/dhcpsrv/mysql_lease_mgr.h

@@ -593,23 +593,7 @@ private:
 
     /// @brief Check Error and Throw Exception
     ///
-    /// Virtually all MySQL functions return a status which, if non-zero,
-    /// indicates an error.  This function centralizes the error checking
-    /// code.
-    ///
-    /// It is used to determine whether or not the function succeeded, and
-    /// in the event of failures, decide whether or not those failures are
-    /// recoverable.
-    ///
-    /// If the error is recoverable, the method will throw a DbOperationError.
-    /// In the error is deemed unrecoverable, such as a loss of connectivity
-    /// with the server, this method will log the error and call exit(-1);
-    ///
-    /// @todo Calling exit() is viewed as a short term solution for Kea 1.0.
-    /// Two tickets are likely to alter this behavior, first is #3639, which
-    /// calls for the ability to attempt to reconnect to the database. The
-    /// second ticket, #4087 which calls for the implementation of a generic,
-    /// FatalException class which will propagate outward.
+    /// This method invokes @ref MySqlConnection::checkError.
     ///
     /// @param status Status code: non-zero implies an error
     /// @param index Index of statement that caused the error