Document chart best practices related to RBAC.

Fixes #3098.

This puts pointers to RBAC and TLS docs in the quickstart guide.

* support output-dir when running 'helm template'

* add --output-dir to documentation

* when writing to file, dont add additional document

* trigger another ci build. make test-unit works for me

* dont write blank files

* return err instead of panic

Add fullnameOverride

k8s client-go closes the ready channel that's passed in (see https://github.com/kubernetes/client-go/blob/master/tools/portforward/portforward.go#L171) This means that Tunnel's Close will always panic, as the client-go library will have closed then channel. This isn't reproducible unless helm.Client is externally, as the helm cli runner doesn't actually invoke Close.

* docs(helm): Document how to update a release idempotently

To use the same command when installing and upgrading a release, using helm upgrade with '--install' works.

Closes #3134

* Upgrade instead of update

feat(http): Add a Helm user-agent string to the http getter

Adding a user-agent to the http getter will enable servers to
distinguish between helm (including various versions) and other
tools connecting to the server.

ref(docs): update plugin install documentation

Increase script portability

Instead of presuming that bash is installed at /bin/bash, use `$PATH`.  Official [bash docker container](https://hub.docker.com/_/bash/) installs bash at `/usr/local/bin` and recommends the use of `env`

Fix incorrect line

bump version to v2.7.2

* fix(helm): add TLS params back

During a recent refactor, several TLS flags stopped being processed for
a few of the commands. This fixes those commands, and documents how to
set up TLS.

* fix(tiller): add stricter certificate verification

The older version of Tiller allowed a weaker set of certificate checks
than we intended. This version requires a client certificate, and then
requires that that certificate be signed by a known CA. This works
around the situation where a user could provide a self-signed
certificate.

Update related.md with new helm-github plugin

Add helm-github plugin to list in documentation

Update best practices on imagePullPolicy

Add previous namespace mismatch warning

Setting the value of `imagePullPolicy` should be aligned to what `helm create` does

fix(helm): home env not set on Windows

When setting $HELM_HOME, only $HOME was considered. This variable is not always present on Windows.

docs(helm): Correct --set to --override in helm init example

fix(tiller): upgrade last deployed release

Fixes #2437

Two bugs were causing this behavior

- Tiller was marking the previous release superseded when an upgrade
failed.
- Upgrade was diffing against failed releases

Documentation on RBAC privileges needed for a helm client

use the latest version of Go/Glide

feat(helm): adding kubeconfig flag

Fix for relative chart path support in index.yaml

use 127.0.0.1 instead of localhost

fix(docs): fix code comment for ReuseValues()