health check is performed in the Nacos startup script

[xuechaos]

A health check is performed in the Nacos startup script to confirm that the startup was successful.

[pguo65535]

this issue is the same purpose for the same corner with #222, tell the absolutely tell those new guy loudly！
"Yes, Nacos server are now start successfully, healthy & happily, you can now go ahead & move forward!!"

[hxy1991]

Stand Alone Mode

• Whether port 8848 is already occupied ?
• ...

Cluster Mode

• Whether port 8848 is already occupied ?
• Whether "cluster.conf" exists and configured correctly ?
• Whether the database connection information is configured in "application.properties" and configured correctly ?
• Whether the database connect successfully ?
• Whether to successfully dump data from the database ?
• ...

[xuechaos]

0.6版本先把健康检查接口做好，按照k8s体系，0.7版本进行集成启动脚本。