ref(cache): just use go. remove bash script

With this change the cache image is just 15MB.
```console
deis/cache             go                   495544d5f703        34 minutes ago      14.25 MB
deis/cache             latest               0da0419a98b6        33 hours ago        255.2 MB
```

Why the use of `FROM busybox:ubuntu-14.04` and not `FROM scratch`?
Unfortunately is not possible to compile redis as a static binary, it depends of the next list of files:
```console
ldd /usr/local/bin/redis-server
	linux-vdso.so.1 (0x00007fff4d3fd000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f49f9213000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f49f900f000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f49f8df1000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f49f8a49000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f49f951a000)
```

this is the only reason. I tried to use `FROM scratch` but is was a waste of time.

The idea of this refactoring is to launch a go app that publish the configuration of the component
to etcd, launch the redis-server binary and redirect the stdout and stderr of the redis process.