feat(helm): remove the requirement that fetch/install need version

[technosophos]

This removes the requirement that a fetch or install command must
explicitly state the version number to install. Instead, this goes to
the strategy used by OS package managers: Install the latest until told
to do otherwise.

Closes #1198

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This change is

[technosophos]

This PR removes the requirement that users supply versions for charts when doing the following operations:

• helm install
• helm inspect
• helm upgrade
• helm fetch

The new format for a chart reference is REPO_NAME/CHART_NAME:

• stable/mariadb
• incubator/mongodb

It is now illegal to supply a version suffix to the chart name (stable/mariadb-0.1.0). To supply a version, use the --version flag:

$ helm install stable/mariadb --version 0.0.9

Other changes in this PR:

• Docs updated
• Additional field added to provenance.Verification to disambiguate which file was verified
• repotest.Server can now replicate a client-side cache (to ease testing)

[technosophos]

Closes #1262

[michelleN]

That's one small step for a helm user, one giant leap for the helm user experience.

[michelleN]

Not a blocker by any means but the first half of the error message is a little unclear.

helm [feat/1198-no-version-required*]$ bin/helm fetch tscharts/alpine --version 3.0.0
Error: chart "alpine" not found in tscharts index. (try 'helm repo update'). No chart version found for alpine-3.0.0

[michelleN]

Manually tested! Looks good.

[adamreese]

probably unrelated, got a mess of extra line returns

% helm install tscharts/alpine
Fetched tscharts/alpine to alpine-0.2.0.tgz
quarreling-but
Last Deployed: Fri Oct  7 10:49:19 2016
Namespace: default
Status: DEPLOYED

Resources:
==> v1/Pod
NAME                       READY     STATUS              RESTARTS   AGE
quarreling-but-my-alpine   0/1       ContainerCreating   0          0s

[adamreese]

manually tested