operator-sdk build does not print stderr

[hasbro17]

Currently running the operator-sdk build command does not show the error output of why a build failed. E.g:

$ operator-sdk build quay.io/coreos/operator-sdk-dev:haseeb
Error: failed to build: (exit status 1)

Whereas the actual error is

$ ./tmp/build/build.sh
building memcached-operator...
pkg/stub/handler.go:6:2: case-insensitive import collision: "github.com/hasbro17/memcached-operator/vendor/github.com/Sirupsen/logrus" and "github.com/hasbro17/memcached-operator/vendor/github.com/sirupsen/logrus"

This is because in commands/operator-sdk/cmd/build.go we don't print the output buffer returned from running the command if it fails. That output buffer holds stderr and so it should be printed in case of error.
https://github.com/coreos/operator-sdk/blob/master/commands/operator-sdk/cmd/build.go#L42-L44

/cc @fanminshi

[hasbro17]

Probably best to double check if this is done anywhere else as well on running a command in commands/operator-sdk/cmd/*

[fanminshi]

good catch! I need to capture the std.err when running subprocess bcmd := exec.Command(build) https://github.com/coreos/operator-sdk/blob/master/commands/operator-sdk/cmd/build.go#L41

[hasbro17]

Yeah just print out the output buffer from o, err := bcmd.CombinedOutput(). That should just contain stderr and stdout.