Fixes issues with building on MacOS 
Fixes issues with building on MacOS 

1. tempfile is unrestricted for docker
```
# Run the build in a container in order to have reproducible builds
# Also, fetch the latest ca certificates
docker run --rm -i -t -v /var/folders/pb/51g49l9x0x59p7qzc0m3qqdr0000gn/T/heapster.XVvw2ydR:/build -v /Users/AlmogBaku/Documents/Projects/golang/src/k8s.io/heapster:/go/src/k8s.io/heapster -w /go/src/k8s.io/heapster golang:1.7 /bin/bash -c "\
		cp /etc/ssl/certs/ca-certificates.crt /build \
		&& GOARCH=amd64 CGO_ENABLED=0 go build -ldflags \"-w -X k8s.io/heapster/version.HeapsterVersion=v1.3.0-alpha.0 -X k8s.io/heapster/version.GitCommit=3e79aa3\" -o /build/heapster k8s.io/heapster/metrics \
		&& GOARCH=amd64 CGO_ENABLED=0 go build -ldflags \"-w -X k8s.io/heapster/version.HeapsterVersion=v1.3.0-alpha.0 -X k8s.io/heapster/version.GitCommit=3e79aa3\" -o /build/eventer k8s.io/heapster/events"
docker: Error response from daemon: Mounts denied: mac/osxfs/#namespaces for more info.
.
x0x59p7qzc0m3qqdr0000gn/T/heapster.XVvw2ydR
is not shared from OS X and is not known to Docker.
You can configure shared paths from Docker -> Preferences... -> File Sharing.
See https://docs.docker.com/docker-for-.
ERRO[0000] error getting events from daemon: net/http: request canceled 
make: *** [container] Error 125
```

This issue occurs since the directory that the `mktemp` creates isn't allowed by the docker. This patch creates the temporary dir under the `tmp` dir, which is allowed.

(reference: https://forums.docker.com/t/getting-mounts-denied-on-previously-working-container-after-upgrading-to-v1-12-0-beta18-3-gec40b14/17546)

2. sed require extra argument
http://stackoverflow.com/questions/16745988/sed-command-works-fine-on-ubuntu-but-not-mac
bruceauyeung/heapster,bluebreezecf/heapster,johanneswuerbach/heapster,AlmogBaku/heapster,andyxning/heapster,adfin/statster,bruceauyeung/heapster,luxas/heapster,johanneswuerbach/heapster,AlmogBaku/heapster,Stackdriver/heapster,burmanm/heapster,huangyuqi/heapster,piosz/heapster,andyxning/heapster,huangyuqi/heapster,adfin/statster,burmanm/heapster,piosz/heapster,luxas/heapster,krzyzacy/heapster,krzyzacy/heapster,Stackdriver/heapster,bluebreezecf/heapster,whuwxl/heapster,whuwxl/heapster