Implement #11832. Add an option to start regrtest and wait for input before continuing.
Implement #11832. Add an option to start regrtest and wait for input
before continuing.

This is useful for starting up the test suite to attach a debugger such
as Visual Studio or others.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator