[SPARK-16536][SQL][PYSPARK][MINOR] Expose sql in PySpark Shell

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR exposes sql in PySpark Shell like Scala/R Shells for consistency.

Background

• Scala

  scala> sql("select 1 a")
  res0: org.apache.spark.sql.DataFrame = [a: int]

• R

  > sql("select 1")
  SparkDataFrame[1:int]

Before

• Python

  >>> sql("select 1 a")
  Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  NameError: name 'sql' is not defined

After

• Python

  >>> sql("select 1 a")
  DataFrame[a: int]

How was this patch tested?

Manual.

[dongjoon-hyun]

Hi, @rxin .
Could you review this trivial PR exposing sql() in PySpark Shell for consistency?

[SparkQA]

Test build #62286 has finished for PR 14190 at commit c5dc235.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[rxin]

Merging in master.

[dongjoon-hyun]

Thank you, @rxin !