Add snapshot support

[Sharpie]

This patchset adds provider actions required by the vagrant snapshot command introduced in Vagrant 1.8.0. The semantics of each action are modeled after the Virtualbox implementation:

https://github.com/mitchellh/vagrant/blob/v1.8.0/plugins/providers/virtualbox/action.rb#L230-L281

The actions make use of Vagrant UI strings introduced in 1.8.0 and are thus surrounded by guard statements to prevent them from being loaded by older Vagrant versions.

[coveralls]

Coverage decreased (-3.9%) to 87.685% when pulling 6339020 on Sharpie:add-snapshot-support into eb06809 on ggiamarchi:master.

[coveralls]

Coverage decreased (-4.3%) to 87.362% when pulling 83dee17 on Sharpie:add-snapshot-support into eb06809 on ggiamarchi:master.

[coveralls]

Coverage decreased (-3.8%) to 87.788% when pulling 599cf79 on Sharpie:add-snapshot-support into 569a7b8 on ggiamarchi:master.

[npwalker]

This is great, I'd love to see this merged!

[ggiamarchi]

Expect the bug on the boolean value in metadata, everything looks good.

[ggiamarchi]

It fails on vagrant snapshot save. The API respond a 400 error because of the boolean true. Replacing it by the string "true" fix it.

==> default: Snapshotting the machine as 'test-snap-01'...
2016-11-15 20:00 | DEBUG | block in create_snapshot - start
2016-11-15 20:00 | DEBUG | request  => method  : POST
2016-11-15 20:00 | DEBUG | request  => url     : http://openstack:8774/v2/f977fe8845974e64a643c9079bd40c3f/servers/86a4d73f-81e9-4ea4-bdf5-e359b1b16855/action
2016-11-15 20:00 | DEBUG | request  => headers : {"X-Auth-Token"=>"13ef9c8931974c0184c0bf62cc5f014b", :accept=>:json, :content_type=>:json}
2016-11-15 20:00 | DEBUG | request  => body    : {"createImage":{"name":"test-snap-01","metadata":{"vagrant_snapshot":true}}}
2016-11-15 20:00 | DEBUG | response => code    : 400
2016-11-15 20:00 | DEBUG | response => headers : {:content_length=>"137", :content_type=>"application/json; charset=UTF-8", :x_compute_request_id=>"req-a1a74fe0-fafe-486b-bc60-76984af9a0c2", :date=>"Tue, 15 Nov 2016 19:00:44 GMT"}
2016-11-15 20:00 | DEBUG | response => body    : {"badRequest": {"message": "Invalid input for field/attribute vagrant_snapshot. Value: True. True is not of type 'string'", "code": 400}}

@Sharpie Does it work in your tests ? Maybe an implementation difference on nova across different OpenStack versions. I ran my tests on an Canonical distribution based on Liberty.

[Sharpie]

I've been running a patched provider that includes these changes against Kilo for a few months now. I don't have another OpenStack installation available to test against, but from the error message it seems like the API schema for metadata may have changed to allow only strings --- I'll see if I can track that down.

[Sharpie]

@ggiamarchi I've updated this patchset to correct the metadata issue and have been running it successfully against OpenStack Mitaka for a couple weeks now.

[coveralls]

Coverage decreased (-3.6%) to 87.6% when pulling 12ab906 on Sharpie:add-snapshot-support into 876ad73 on ggiamarchi:master.

[npwalker]

@ggiamarchi I created my own gem with @Sharpie's changes and I'm using it successfully. Is there anything preventing a merge?