Test ipfs2 with sharness

@maybebtc @jbenet 

The goal of this branch is to help make the sharness tests pass with ipfs2.
It can be merged into a test branch in jbenet/go-ipfs, so that we can see what happens on travis. 

The first patch in this PR is https://github.com/jbenet/go-ipfs/commit/3368d293eaad0d30dda9aa10557ae925c7443a5e. It was made by @maybebtc to make the sharness tests use ipfs2.

The second patch make the output of some tests match the output from some ipfs2 commands. It's possible we should instead change the output from the ipfs2 commands to match the tests, or that we should change both the tests and the output from ipfs2.