Allow reading a message from failure tag

[janisz]

Consider following example. Currently there is no way to read CDATA from <failure>...</failure> tag.

	<testsuite name="github.com/stackrox/rox/central/resourcecollection/datastore/store/postgres" tests="1" failures="1" errors="0" id="78" hostname="merge-go-postgres-tests-stackrox-initial" time="2.751" timestamp="2022-10-11T13:32:27Z">
		<properties>
			<property name="coverage.statements.pct" value="49.00"></property>
		</properties>
		<testcase name="TestCollectionsStore" classname="github.com/stackrox/rox/central/resourcecollection/datastore/store/postgres" time="2.330">
			<failure message="Failed"><![CDATA[    env_isolator.go:41: EnvIsolator: Setting ROX_POSTGRES_DATASTORE to true]]></failure>
		</testcase>
	</testsuite>