Fix linode-cli linodes create operation

[Dorthu]

In testing an unrelated CLI change, I noticed this:

$ linode-cli linodes create --help
linode-cli linodes create
Linode Create

Arguments:
  --root_pass: This will set the root user's password on the newly-created Linode.
  --stackscript_id: A StackScript ID that will cause the referenced StackScript to be run duringdeployment of this Linode.
  --authorized_keys: A list of public SSH keys that will be automatically appendedto the root user's `~/.
  --authorized_users: A list of usernames.
  --stackscript_data: This field is required only if the StackScript being deployed requires inputdata from the User for successful completion.
  --booted: This field defaults to `true` if the Linode is created with an Image or from a Backup.
  --image: An Image ID to deploy the Disk from.

That's not good - the linodes create operation is missing many
parameters, including type and region that are required. After some
digging, I determined that it was because the allOf in
/linodes/instances.post.requestBody.content.application/json.schema
section was not nested properly; the schema should be all of the
references LinodeRequest and the given properties. Having an
allOf alongside properties isn't really correct (although it's
apparently not invalid).

Built off this spec, the CLI now see the full request:

$ python -m linodecli linodes create --help
linode-cli linodes create
Linode Create

Arguments:
  --region: (required) The [Region](/docs/api/regions/#regions-list) where the Linode will be located.
  --type: (required) The [Linode Type](/docs/api/linode-types/#types-list) of the Linode you are creating.
  --interfaces.label: The name of this interface.
  --root_pass: This will set the root user's password on the newly-created Linode.
  --backup_id: A Backup ID from another Linode's available backups.
  --group: A deprecated property denoting a group label for this Linode.
  --stackscript_id: A StackScript ID that will cause the referenced StackScript to be run duringdeployment of this Linode.
  --authorized_keys: A list of public SSH keys that will be automatically appendedto the root user's `~/.
  --stackscript_data: This field is required only if the StackScript being deployed requires inputdata from the User for successful completion.
  --image: An Image ID to deploy the Disk from.
  --tags: An array of tags applied to this object.
  --backups_enabled: If this field is set to `true`, the created Linode will automatically beenrolled in the Linode Backup service.
  --label: The Linode's label is for display purposes only.
  --interfaces.purpose: The type of interface.
  --private_ip: If true, the created Linode will have private networking enabled and assigned a private IPv4 address.
  --swap_size: When deploying from an Image, this field is optional, otherwise it is ignored.
  --interfaces.ipam_address: This Network Interface's private IP address in Classless Inter-Domain Routing (CIDR) notation.
  --authorized_users: A list of usernames.
  --booted: This field defaults to `true` if the Linode is created with an Image or from a Backup.

I could be persuaded that the CLI's spec parser is incorrectly merging
the allOf with the same-level properties, but I do not believe this
is the case. The OpenAPI Specification is light on details here, but
all examples using allOf do not include sibling nodes like this.

[Dorthu]

I pointed this at master since the CLI's linode create operation is presently broken - I could point it back at development if you prefer.

[leslitagordita]

@bbiggerr I pulled this down and built the site locally and it lgtm. @Dorthu has requested that we get this out with tomorrow's release.