Since go1.8 GOPATH is not required to set prior, as
it defaults to "${HOME}/go" we only need to check if
go tool detected GOPATH correctly. If yes then we
proceed if not we fail.
Golang 1.6 is default version for the build now.
Additionally set 'GODEBUG=cgocheck=0' for now, until
we fix the erasure coding package.
Readmore here https://tip.golang.org/doc/go1.6#cgo
