[SPARK-14749][SQL, Tests] PlannerSuite failed when it run individually

[sbcd90]

What changes were proposed in this pull request?

3 testcases namely,

"count is partially aggregated"
"count distinct is partially aggregated"
"mixed aggregates are partially aggregated"

were failing when running PlannerSuite individually.
The PR provides a fix for this.

How was this patch tested?

unit tests

(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

[rxin]

cc @marmbrus

[marmbrus]

OK to test

[sbcd90]

Jenkins test this please

[SparkQA]

Test build #2837 has finished for PR 12532 at commit 5f5238e.

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

[sbcd90]

Hi @rxin ,

Can this be merged?

[rxin]

Merging in master. Thanks.