Table: Unify the creation of Batch and single op requests

[jcookems]

The REST request for a single table operation (for example, updateEntity) should be the same as the MIME part of a batch request containing the same operation.

However, the current Table service implementation had two separate code paths for generating those requests:

updateEntity 
-> putOrMergeEntityCore 
    -> (code for building headers and constructing body)
batch(InsertEntityOperation)
-> createBatchRequestBody
    -> createBatchInsertOrUpdateEntityPart
        -> (code for building headers and constructing body)

To simplify the code, reduce maintenance costs, and ensure consistency between single ops and batch, both code paths should end up in the same function.

[gcheng]

this part is actually odata.

[gcheng]

at the time of updating these methods, will may do them. close for now.