fix(helm): modify `helm repo update` help info

The former help info may cause misunderstanding that this command
can update content of charts existing in remote respositories while
it does pull charts' info from remote repositories.

This trivial modification leads better understanding.

fix(helm): fix race conditions in flag parsing

fix(helm): prepend repo URL to packages missing scheme

fix(2452): sort templates before parse

docs(helm): fix typo

adjust the check parameter order for uninstall 

fix(docs): A couple spelling mistakes on chart_tests.md

GitHub got more fussy about markdown

Fix typo: Update using_helm.md

bump download links to 2.4.2

they are currently set to 2.4.1.

Missed these on my PR last night

fix(docs): Updated non-working example in 'Using Helm' documentation

fix(docs): Fixing mariadb spelling mistake

Closes #2527

fix(plugins): exists --> exist

fix(tiller): Adds missing import back

PR #2513 was behind master when merged. Other commits were
added that required the use of the log package. This re-adds
that package.

feat(tiller): Adds more logging

This builds on previous work and adds more logging to follow
the full process of installing, updating, deleting, and rolling back.
This also standardizes capitalization of logs and small formatting
fixes

* fix a number of issues with flag parsing
* add support for `HELM_DEBUG`
* lazy expand flag default envars

Add --force to upgrade and rollback to delete/create when conflicts

This sorts templates by depth before sending them to the template
parser. Deepest templates are parsed first, with umbrella templates
parsed last. Since template definition names are LIFO, that means that
the highest level templates will claim the namespace.

Or, to put it simply, you can predictably override a child's defined
template by re-defining it in a parent chart.

Closes #2452

When a repository is generated without --url, the packages in that
repository do not have FQDNs. In this case, the URL prefix (FQDN plus
base path) should be derived from the repository's base URL. This seems
to be a regression that crept in around Helm 2.2.0. This is now fixed.

Closes #2315
Closes #2510

Check existence of $HELM_HOME/plugins before installing plugin

Adds alias for dependencies

fix(docs): Remove "no nested globals allowed"

Add check to stop helm 'waiting' for external services to become ready

Remove incorrect statements in charts.md about nested globals not being allowed.