SAMZA-2694: Always show stack traces on gradle failures

[bringhurst]

CI build failures are more useful when they show stack traces by default.

[bringhurst]

It appears to work. For example, it shows the following in the latest build failure:

testStopBehavior FAILED
825
    java.lang.AssertionError: Timed out waiting for listener to be give 5 updates
826
        at org.junit.Assert.fail(Assert.java:88)
827
        at org.apache.samza.container.host.TestStatisticsMonitorImpl.testStopBehavior(TestStatisticsMonitorImpl.java:91)
828

829
testPhysicalMemoryReporting FAILED
830
    java.lang.AssertionError: Timed out waiting for listener to be give 5 updates
831
        at org.junit.Assert.fail(Assert.java:88)
832
        at org.apache.samza.container.host.TestStatisticsMonitorImpl.testPhysicalMemoryReporting(TestStatisticsMonitorImpl.java:51)
833

834
> Task :samza-kafka_2.11:test
835

836
> Task :samza-core_2.11:test
837

838
testAllEntries FAILED
839
    java.lang.OutOfMemoryError: Java heap space
840
        at org.apache.commons.lang3.ArrayUtils.subarray(ArrayUtils.java:7934)
841
        at org.apache.samza.zk.ZkMetadataStore.chunkMetadataStoreValue(ZkMetadataStore.java:189)
842
        at org.apache.samza.zk.ZkMetadataStore.put(ZkMetadataStore.java:111)
843
        at org.apache.samza.zk.TestZkMetadataStore.testAllEntries(TestZkMetadataStore.java:120)

[kw2542]

LGTM