Synchronize submodules

This makes "repo sync" initiate and update submodules for stoq, stoqdrivers and
kiwi. Also, make the number of jobs (the number of projects fetched at the same
time) 4 by default. This makes sync a lot faster!

Change-Id: I4d9788c84ec3a35c16c5dfac59ff1e4b0a18a350