* fix(helm): fix golint warning due to ApiVersionV1 constant name

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

* fix(helm): fix golint warning due to ResolveChartVersionAndGetRepo comment

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

* fix(helm): fix golint warnings on HttpGetter type and SetCredentials method missing a comment

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

* fix(helm):fix golint warning due to comment on FindChartInAuthRepoURL function

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

* fix(helm): fix golint warning due to RepoFile type name

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

* fix(helm): fix golint warning due to ParseString comment

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

Authentication support for remote charts repositories.

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.

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

This flattens the getter package tree, adds tests, and changes a little
bit of the terminology to follow Go idioms. This also makes much of the
getter API private to begin with. This will give us more flexibility in
the future.

It is now possible to create plugins with chart download capabilities for custom, non-http protocols.
Furthermore it is possible to reuse helm packages to implement alternative clients with these custom downloader functions.