JDWP: fix flaky test StackFrame.GetValues002Test

Fixes flaky StackFrame.GetValues002Test#testGetValues009_ThisObject
caused by incorrect synchronization between test and debuggee.

The "start" synchronization moves to internalSetup method (called
before executing the test method) and the "end" synchronization
moves to internalTearDown method.

Bug: 19999218
Change-Id: I38d7f33b639c0b4ec9f0be6e8a8a505251ced3b4