JDBC: Provide an option to simplify beeline usage by supporting default and named URL for beeline

Currently, after opening Beeline CLI, the user needs to supply a connection string to use the HS2 instance and set up the jdbc driver. Since we plan to replace Hive CLI with Beeline in future (HIVE-10511), it will help the usability if the user can simply type beeline and get start the hive session. The jdbc url can be specified in a beeline-site.xml (which can contain other named jdbc urls as well, and they can be accessed by something like: beeline -c namedUrl. The use of beeline-site.xml can also be potentially expanded later if needed.