Don't use single letter catch variables

Update existing catch blocks to ensure that `ex` is always used
in preference to `e` or `t` as the variable name.

Issue: SPR-16968

spring-test/src/main/java/org/springframework/test/web/servlet/DefaultMvcResult.java

@@ -160,7 +160,7 @@ class DefaultMvcResult implements MvcResult {
 		try {
 			return this.asyncDispatchLatch.await(timeout, TimeUnit.MILLISECONDS);
 		}
-		catch (InterruptedException e) {
+		catch (InterruptedException ex) {
 			return false;
 		}
 	}