[SPARK-21977][HOTFIX] Adjust EnsureStatefulOpPartitioningSuite to use scalatest lifecycle normally instead of constructor

[srowen]

What changes were proposed in this pull request?

Adjust EnsureStatefulOpPartitioningSuite to use scalatest lifecycle normally instead of constructor; fixes:

*** RUN ABORTED ***
  org.apache.spark.SparkException: Only one SparkContext may be running in this JVM (see SPARK-2243). To ignore this error, set spark.driver.allowMultipleContexts = true. The currently running SparkContext was created at:
org.apache.spark.sql.streaming.EnsureStatefulOpPartitioningSuite.<init>(EnsureStatefulOpPartitioningSuite.scala:35)

How was this patch tested?

Existing tests

[srowen]

CC @brkyvz

[SparkQA]

Test build #82032 has started for PR 19306 at commit af017f0.

[brkyvz]

Thanks @srowen . LGTM!

[SparkQA]

Test build #3928 has finished for PR 19306 at commit af017f0.

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

[srowen]

Merged to master