Relicense as MPLv2

[misterbisson]

@jen20's #5 will eliminate the GPL dependencies in this repo and is required before this can be merged.

This PR simply relicenses the repo to address the following:

• License #6
• License gosign#4 (where this is included as a dependency)
• provider/triton: New provider for Joyent Triton hashicorp/terraform#5277 (comment) (which was blocked because of the license here)

With precedent from TritonDataCenter/gosdc#11, which explains:

gosdc was mistakenly licensed as LGPL: LGPL is not a license that we at Joyent use for de novo software, and (bluntly) no one noticed that this wasn't licensed as MIT (our preference for node modules) or MPLv2 (our preference for entirely new work). While having a few external contributors, Joyent has retained copyright, and we are therefore making the decision to relicense gosdc as MPLv2 as per our own policy. We are believers in the MPLv2 because we believe that it captures the spirit of the LGPL but with much less ambiguity (and therefore in a way that is much more palatable for integration into larger works) -- so hopefully those external contributors (specifically, @wallyworld and @BrianHicks) who contributed to gosdc as an LGPL project won't feel wronged by the fact that it's now an MPLv2 one!

This repo includes work from the following contributors:

• @dstroppa
• @richardiux
• @wallyworld
• @BrianHicks

This was an oversight in TritonDataCenter/gosdc#11 and is part of some license cleanup triggered by hashicorp/terraform#5277 and https://twitter.com/jen20/status/682579140466323458 before that.

[dwlf]

IANAL, but on further consideration as MPLv2 is a file-level copyright license, the update should include an update to all source files like:

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

This also leads directly into a copyright bump to Copyright (c) 2016 Joyent Inc. to round out the picture.