We currently build binaries for all targets into bin.
This makes mess in bin/ and does not allow testing of different archs.
Build target binaries into bin/OS_ARCH/ subdirs.
Host binaries are still built into bin/.
Update #333
Update #324
Update #191
For https://github.com/golang/go/issues/21337.
Since the introduction of aliases is in Go1.9 but Go1.9 hasn't
yet been officially released, let's use go1.9rc1 which is supported
on Travis CI by their Go version getter gimme
https://github.com/travis-ci/gimme
instead of against go1.8.1. This solves the problem on which
our vendored code is updated using Go1.9* syntax but is running
against Go1.8* in Travis CI tests.
