Hide log for dependencies installs in travis

Travis was erroring because it ran too long without output when we installed all of our dependencies, and #690 fixed this by splitting out all the builds *and* making them verbose.  Unfortunately, that also balloned our travis logs with lots of info about building scipy and h5py (which we don't care about).

This PR silences the optional dependency builds.  But it keeps the change in #690 of splitting out the dependecy builds to run separately one at a time.  Each one individually is < 5 min, so Travis is kept happy.  But now our log is ~1k lines instead of 10k.