SUREFIRE-1028 Unable to run single test (junit)

Fix for a critical bug:
https://jira.codehaus.org/browse/SUREFIRE-1028

Fixed in subclass `FilterFactory.MethodFilter`.
The nested children need to be scanned with filtering conditions.
The PC uses aggregared structure of JUnit Runners and therefore filtered test methods should be scanned in whole hierarchy.

Problem of this bug: No tests to execute while parallel execution is triggered on filtered test method (see single-test.apt.vm).
`mvn test -Dtest=SomeTest#test`
Plugin configuration:
parallel='classes', useUnlimitedThreads=true