[SPARK-14412][.2][ML] rename *RDDStorageLevel to *StorageLevel in ml.ALS

## What changes were proposed in this pull request?

As discussed in #12660, this PR renames
* intermediateRDDStorageLevel -> intermediateStorageLevel
* finalRDDStorageLevel -> finalStorageLevel

The argument name in `ALS.train` will be addressed in SPARK-15027.

## How was this patch tested?

Existing unit tests.

Author: Xiangrui Meng <meng@databricks.com>

Closes #12803 from mengxr/SPARK-14412.