tests(sharness) attempt to execute sharness tests on ipfs2

@jbenet @chriscool (not to be merged into master) This is a hack to run sharness tests on th ipfs2 binary. Instead of compiling cmd/ipfs, it compiles cmd/ipfs2 and copies this into test/bin/ipfs. I thought this would be enough to pass the `basic-commands` test, but it's not. Although the output is fairly similar, the `ipfs version` test fails. ``` test (feat/test2) λ. diff version1 version2 1c1 < ipfs version 0.1.7 --- > ipfs version 0.1.5 ``` I'm not very experienced with `sh` scripting, so perhaps I'm missing a key ingredient or maybe misunderstanding the the tests are meant to work. Would like to get input on this. Thanks, @maybebtc