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`

HELM_TMP_ROOT directory is now uniquely generated to avoid potential clashes with old installation instances or other processes using the same /tmp subdirectory

https://circleci.com/docs/2.0/configuration-reference/#deploy

Currently the bash script that installs Helm is hard-coded to use
openssl sha command but some distros like Debian 9 only have sha1.
Since the popular current distros have sha1 we can switch to that.

Closes(#2859)

Do not close the pipe early, output only the first version found.  wget command changed for consistency.
Fixes #2802

$EUID is readonly, so it should be save to test against it.

Thanks for the tip @thomastaylor312 !

Avoid using $* multiple times

If the execution user is already the root user, this avoids requireing
sudo to be installed within the environment. Which might helo in CI
environments.

2.4.0 stopped installing development versions by default. This allows
the user to re-enable that support by setting --devel.

Closes #2407

* Adds update option to plugin command

Fixes issues/2385 - helm install silently updates the plugin, if it pre-existed

* Added tests for new methods for plugin update

* Updated docs

* Updated review comments :)

* Return error exit code when there is error

helps with half of #2224

Updated the 'helm completion' command to take in the shell
as a parameter. Currently acceptable options are 'bash' and
'zsh'. Also fixed the completions to work with zsh in a manner
similar to what kubectl does.

Also updated the docs to reflect this change.

Closes #2201

Rebase on kubernetes v1.6

gosimple seems to be eating all memory in CircleCI.  Testing disabling
the check to see if CI builds.

This change prevents downloading the same version as already installed.