[SPARK-17408][TEST] Flaky test: org.apache.spark.sql.hive.StatisticsSuite

### What changes were proposed in this pull request?
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/64956/testReport/junit/org.apache.spark.sql.hive/StatisticsSuite/test_statistics_of_LogicalRelation_converted_from_MetastoreRelation/
```
org.apache.spark.sql.hive.StatisticsSuite.test statistics of LogicalRelation converted from MetastoreRelation

Failing for the past 1 build (Since Failed#64956 )
Took 1.4 sec.
Error Message

org.scalatest.exceptions.TestFailedException: 6871 did not equal 4236
Stacktrace

sbt.ForkMain$ForkError: org.scalatest.exceptions.TestFailedException: 6871 did not equal 4236
	at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:500)
```

This fix does not check the exact value of `sizeInBytes`. Instead, we compare whether it is larger than zero and compare the values between different values.

In addition, we also combine `checkMetastoreRelationStats` and `checkLogicalRelationStats` into the same checking function.

### How was this patch tested?
N/A

Author: gatorsmile <gatorsmile@gmail.com>

Closes #14978 from gatorsmile/spark17408.