<rdar://problem/15367122>

Fixed the test case for "test/functionalities/exec/TestExec.py" on Darwin.

The issue was breakpoints were persisting and causing problems. When we exec, we need to clear out the process and target and start fresh with nothing and let the breakpoints populate themselves again. This patch correctly clears out the breakpoints and also flushes the process so that the objects (process/thread/frame) give out valid information.