docker: Make sure that we properly check for containers.

Makefile

@@ -138,7 +138,7 @@ install: gomake-all
 
 dockerimage: checkdocker verifiers $(UI_ASSETS)
 	@echo "Building docker image:" minio:$(TAG)
-	@GO15VENDOREXPERIMENT=1 go build --ldflags $(DOCKER_LDFLAGS) -o minio.dockerimage
+	@GO15VENDOREXPERIMENT=1 GOOS=linux GOARCH=amd64 go build --ldflags $(DOCKER_LDFLAGS) -o minio.dockerimage
 	@mkdir -p export
 	@sudo docker build --rm --tag=minio/minio:$(TAG) .
 	@rmdir export

runtime-checks.go

@@ -29,12 +29,12 @@ import (
 // isContainerized returns true if we are inside a containerized environment.
 func isContainerized() bool {
 	// Docker containers contain ".dockerinit" at its root path.
-	if _, e := os.Stat("/.dockerinit"); os.IsNotExist(e) {
+	if _, e := os.Stat("/.dockerinit"); e == nil {
 		return true
 	}
 
 	// Check if cgroup policies for init process contains docker string.
-	if cgroupData, e := ioutil.ReadFile("/proc/1/cgroup"); e != nil {
+	if cgroupData, e := ioutil.ReadFile("/proc/1/cgroup"); e == nil {
 		if strings.Contains(string(cgroupData), "/docker-") {
 			return true
 		}