to spawn an lldb child command.  The test is not "correct" in that the '** Stop Hooks **'
message emitted by the Target implementation is invoked asynchronously and is using a separate:

    CommandReturnObject result;

command return object that what the driver passes to the normal command interpreter loop.
But it can help test our output serialization work.

I need to modify the test case later to maybe only test that "-o 'expr ptr'" option does indeed work.

llvm-svn: 130742