Rename centos test-kitchen platform

[patcon]

CentOS minor version floats:
https://unix.stackexchange.com/questions/60660/minor-upgrades-and-version-numbers-on-centos

More consistent to just call it centos-6. (For example, providers like DigitalOcean offer images of 6.5)

[martinb3]

For a while, the kitchen-rackspace driver didn't support this, when Rackspace dropped minor version information from its images. It does again, now, though. Thanks @patcon!

[martinb3]

@patcon Are you sure the latest kitchen-vagrant supports this as well? I updated and it appears to be broken now. I'm wondering if maybe they removed the images from the S3 bucket.

>>>>>> ------Exception-------
>>>>>> Class: Kitchen::ActionFailed
>>>>>> Message: Failed to complete #create action: [Expected process to exit with [0], but received '1'
---- Begin output of vagrant up --provider virtualbox ----
STDOUT: Bringing machine 'default' up with 'virtualbox' provider...
==> default: Box 'opscode-centos-6' could not be found. Attempting to find and install...
    default: Box Provider: virtualbox
    default: Box Version: >= 0
==> default: Adding box 'opscode-centos-6' (v0) for provider: virtualbox
    default: Downloading: https://opscode-vm-bento.s3.amazonaws.com/vagrant/virtualbox/opscode_centos-6_chef-provisionerless.box

STDERR: An error occurred while downloading the remote file. The error
message, if any, is reproduced below. Please fix this error and try
again.

The requested URL returned error: 404 Not Found
---- End output of vagrant up --provider virtualbox ----

[patcon]

Ah grr... I was careless in my thinking Martin, so apologies: I neglected that you were depending on kitchen-vagrant's assumptions. I was submitting what was in my mind a totally minor naming change, not realizing kitchen-vagrant was being clever with it.

But given how centos upgrades work, I will submit a PR there. (chef/bento#406)

[patcon]

And sorry for the noise Martin. Glad you tested :)