fixed making proper target in docker


DEMO:
```
~/src/europa/src/golang/src/github.com/zenoss/zminion
# plu@plu-9: make docker-tgz
...
Step 10 : RUN go get github.com/tools/godep
 ---> Using cache
 ---> 7401f1d5e592
Successfully built 7401f1d5e592
docker run --rm -v `pwd`:/go/src/github.com/zenoss/zminion -w /go/src/github.com/zenoss/zminion -e DUID=1000 -e DGID=1000 zenoss/zminion-build:0.1.0 make tgz
godep go build -ldflags "-X main.Version 0.1.0 -X main.Gitcommit 'bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb' -X main.Gitbranch 'feature/TA22293' -X main.Date 'Thu Sep  4 17:24:16 UTC 2014' -X main.Buildtag '0'"
chown 1000:1000 zminion
mkdir -p /tmp/zminion-pkgroot-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb/usr/bin
cp -v zminion /tmp/zminion-pkgroot-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb/usr/bin
'zminion' -> '/tmp/zminion-pkgroot-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb/usr/bin/zminion'
tar cvfz /tmp/zminion-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb.tgz -C /tmp/zminion-pkgroot-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb/usr .
./
./bin/
./bin/zminion
chown 1000:1000 /tmp/zminion-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb.tgz
mv /tmp/zminion-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb.tgz .


~/src/europa/src/golang/src/github.com/zenoss/zminion
# plu@plu-9: ls -l
total 9952
-rwxrwxr-x 1 plu plu     236 Sep  4 12:22 gitstatus.sh
drwxrwxr-x 3 plu plu    4096 Sep  4 12:22 Godeps
drwxrwxr-x 2 plu plu    4096 Sep  4 12:22 hack
-rw-rw-r-- 1 plu plu   18026 Aug 29 11:03 LICENSE
-rw-rw-r-- 1 plu plu    8788 Sep  4 12:22 main.go
-rw-rw-r-- 1 plu plu    3632 Sep  4 12:23 makefile
-rw-rw-r-- 1 plu plu      67 Aug 29 11:03 README.md
-rw-rw-r-- 1 plu plu       6 Sep  4 12:22 VERSION
-rwxr-xr-x 1 plu plu 7953344 Sep  4 12:24 zminion
-rw-r--r-- 1 plu plu 2176722 Sep  4 12:24 zminion-bf286e5a6dfd95ec0cb0ab5a00b4f1c3bf2939cb.tgz

~/src/europa/src/golang/src/github.com/zenoss/zminion
# plu@plu-9: make clean
go clean
rm -f *.deb
rm -f *.rpm
rm -f *.tgz
rm -fr /tmp/zminion-pkgroot-*

~/src/europa/src/golang/src/github.com/zenoss/zminion
# plu@plu-9: ls -l
total 56
-rwxrwxr-x 1 plu plu   236 Sep  4 12:22 gitstatus.sh
drwxrwxr-x 3 plu plu  4096 Sep  4 12:22 Godeps
drwxrwxr-x 2 plu plu  4096 Sep  4 12:22 hack
-rw-rw-r-- 1 plu plu 18026 Aug 29 11:03 LICENSE
-rw-rw-r-- 1 plu plu  8788 Sep  4 12:22 main.go
-rw-rw-r-- 1 plu plu  3632 Sep  4 12:23 makefile
-rw-rw-r-- 1 plu plu    67 Aug 29 11:03 README.md
-rw-rw-r-- 1 plu plu     6 Sep  4 12:22 VERSION

```