Splitting reparenting commands out of vtctl.

So they're easier to disable by just not compiling
this module.
Fixing typo.
Checkpoint or resharding user work.

Now the user used to apply logs is vt_dba (need SUPER).
Adding some disabled code to have a stream of data during
resharding to exercise the reparenting (disabled for
now, it fails).
Fixing permissions in tests.

The 'app' user should be vt_app. It didn't work before, as some
tests expected to be able to drop tables, and that wasn't allowed.
So I changed the permissions so vt_app can drop tables, and use
the user for the tests. It's just not SUPER.
Adding back default user.
Merge branch 'master' into resharding