[SPARK-4930][SQL][DOCS]Update SQL programming guide, CACHE TABLE is eager

`CACHE TABLE tbl` is now __eager__ by default not __lazy__

Author: luogankun <luogankun@gmail.com>

Closes #3773 from luogankun/SPARK-4930 and squashes the following commits:

cc17b7d [luogankun] [SPARK-4930][SQL][DOCS]Update SQL programming guide, add CACHE [LAZY] TABLE [AS SELECT] ...
bffe0e8 [luogankun] [SPARK-4930][SQL][DOCS]Update SQL programming guide, CACHE TABLE tbl is eager