Update the test logging to include the failed assertion

[dlvenable]

Description

The current output of failures shows where the assertion failed. But, it does not show what was wrong with the assertion.

For example, we see logs like this:

AbstractSinkTest > testSinkNotReady() FAILED
    org.opentest4j.AssertionFailedError at AbstractSinkTest.java:84

This change outputs the actual cause without adding the whole stack trace either.

Here is some sample code:

public class ForceFail {
    @Test
    void always_fails() {
        assertThat(true, equalTo(false));
    }
}

The logging includes:

> Task :data-prepper-api:test

ForceFail > always_fails() FAILED
    java.lang.AssertionError:
    Expected: <false>
         but: was <true>

1133 tests completed, 1 failed, 2 skipped

Issues Resolved

N/A

Check List

• New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[oeyh]

Thanks!