Update releases to reflect v1.5.0-beta.1

Before this change, the binary was named `minikube-linux-amd64`,
which is the platform specific artifact name.

When installed through the .deb package, a user expects to have
the `minikube` directly on the `$PATH`.

This change populates the binary as `minikube` in the resulting .deb file.

The makefile was slightly broken for minikube-iso.  Since it && all the
commands to check if buildroot, the git clone failed if the buildroot
folder already existed and broke the target.  I put this logic in a
conditional.

Removes the vendored in kube2sky built into the minikube binary and
replaces the dns solution with kube-dns cluster addon.  This will allow
users to swap out DNS implementations by simply turning off the
kube-dns addon.

updated docs.

We are using k8s pkg/version in minikube cmd to print out the
default version.  This was falling back to the defaults in pkg/version/base.go which were an ugly format string.  This wasn't actually being passed into cluster.go because we didn't pass the string in if was a default version.

Fixed .deb file make target, there was an issue in that git does not track empty directories which the template dir had and the build relied on.  Dir creation is now done in Makefile

Also add notes to the RELEASING.md doc, and a make target to test the release.

files.  Updated to reflect talk regarding creating .deb for kubectl.
Added make deb in Makefile.

url) and to copy files from host to the vm instead of curl within vm.
Also made it so that sshutil.Transfer is done via a Reader.

This broke during the last Makefile cleanup, we were ln'ing the same path to itself.

Cutting v0.6.0 release.  Bumped version in Makefile and releases.json.  Added v0.6.0 to CHANGELOG.md