ToolRunner added in CASSANDRA-15942 stdErr checks improvements

The JVM will output to stderr on some environments to show what flags that were picked up, when this happens all tests which validate stderr start to fail. This was found in the org.apache.cassandra.tools.ClearSnapshotTest as it switched to use the ToolRunner; below is a sample failure on my laptop (I had to modify the asserts since they don’t include the input)

java.lang.AssertionError: 
Expecting empty but was:<"Picked up _JAVA_OPTIONS: -Djava.net.preferIPv4Stack=true
">

	at org.apache.cassandra.tools.ToolRunner.assertEmptyStdErr(ToolRunner.java:339)
	at org.apache.cassandra.tools.ToolRunner.waitAndAssertOnCleanExit(ToolRunner.java:334)
	at org.apache.cassandra.tools.ClearSnapshotTest.testClearSnapshot_RemoveMultiple(ClearSnapshotTest.java:91)

Here _JAVA_OPTIONS is used globally on my system so fails the test; there is also JAVA_TOOL_RUNNER which is used the same way.