Allow proper checkout of repos with submodules.
Allow proper checkout of repos with submodules.

Summary:
Every new employee has had a problem with `.git` not a directory, or
something.

It turns out the problem is that we call `git submodule init` and then
`git submodule status --recursive`.  But we can't recurse until the
submodules are actually synced (and we know what submodules they
contain)!

One solution would be to drop the `--recursive`, but it's there for a
reason.  The other solution is to just sync the submodules at
clone-time, rather than just init-ing them.

I have no idea why we were init-ing rather than syncing before.  It's
not like we're cloning into a bare repo.

While in the area, I also fixed up the submodule call to respect
`--quiet`.

Test Plan:
I ran
   devtools/ka-clone/bin/ka-clone git@github.com:Khan/beep-boop
This succeeded after my change, while failing before.

Reviewers: benkraft

Reviewed By: benkraft

Subscribers: andrew

Differential Revision: https://phabricator.khanacademy.org/D50813

Khan/ka-clone,Khan/ka-clone