[SPARK-21213][SQL][FOLLOWUP] Use compatible types for comparisons in compareAndGetNewStats

[maropu]

What changes were proposed in this pull request?

This pr fixed code to compare values in compareAndGetNewStats.
The test below fails in the current master;

    val oldStats2 = CatalogStatistics(sizeInBytes = BigInt(Long.MaxValue) * 2)
    val newStats5 = CommandUtils.compareAndGetNewStats(
      Some(oldStats2), newTotalSize = BigInt(Long.MaxValue) * 2, None)
    assert(newStats5.isEmpty)

How was this patch tested?

Added some tests in CommandUtilsSuite.

[maropu]

nitpicking though, could you check? @gatorsmile @wzhfy @mbasmanova

[SparkQA]

Test build #86019 has finished for PR 20245 at commit 473b37a.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[maropu]

retest this please

[SparkQA]

Test build #86024 has finished for PR 20245 at commit 473b37a.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[maropu]

retest this please

[SparkQA]

Test build #86029 has finished for PR 20245 at commit 473b37a.

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

[srowen]

Do these values actually take on values larger than Long.MaxValue?

[maropu]

yea, it's a super corner-case (almost impossible). So, this is just a correctness issue as intellij suggests incompatible comparisons. (Actually, I'm not sure why we use BigInt for the statistics for Long)

[gatorsmile]

LGTM

Although this PR is to fix a corner case, we still should clean it.

Thanks! Merged to master/2.3