Implement changing instance type

[WilliamMcCumstie]

When deploying a node, it will spin up with the instance given by the template. However this requires spinning up large (expensive) instances during testing. Instead the ability to spin up a cheap (small) instance for testing is desirable.

This requires the following steps:

1. The change_instance_type method
   This needs to be implemented in three places:

Cloudware::Provider::Base::Machine#change_instance_type => raise NotImplementedError
Cloudware::Provider::AWSInterface::Machine#change_instance_type => aws implementation
Cloudware::Provider::AzureInterface::Machine#change_instance_type => azure implementation

2. This method then needs to be hooked into the Models::Machine or Models::Node. See Remove tagging and Models::Machine #247 for details. For consistency, it should be implemented on Models::Machine until it is removed.

3. A instance_type field needs to be added to Models::Node. This records what the instance should be at the end of deploy

4. When the Models::Node#deploy method is called, it should fire the template off to the provider. Hang for a response, and then initiate the instance type modify. The instance_type should be obeyed on deploy!.

5. A modify-type command needs to be added to the CLI, similar to the power commands. It should work with both a single and group of nodes.

[ColonelPanics]

A few thoughts on usability/user-facing implementation are below but I am open to other ideas for getting this to work

General Specs

• Set/change instance type of nodes
  • Set at deploy time (e.g. flight cloud deploy node01 --instance-type c4.large or flight cloud deploy node01 -p "instance-type=c4.large")
  • Modify running instances (e.g. flight cloud modify node01 --instance-type c4.large)
  • Potentially use instance type maps for provider-agnostic names and consistency of CLI
• Display available instance types
  • Could be provider-specific or a generic map of names (e.g. compute.large would be platform-generic instance type)
• Limit available instance types by group

Instance Type as Parameter

• Can specify instance type on deploy/create (%instancetype%)
• Modify instance type updates metadata parameter value for instance type for consistency's sake

Instance Type Map

• Consistent instance type names between providers
• More human readable, clearer to end-user what they're using
• Allows for group restriction/whitelisting

compute:
  tiny: 
    aws: 'c4.large'
    azure: 'Standard_F2s'
    groups: 'login,nodes,compute,all'
  small:
    aws: 'c4.xlarge'
    azure: 'Standard_F4s'
    groups: 'login,nodes,compute,all'
  medium:
    aws: 'c4.2xlarge'
    azure: 'Standard_F8s'
    groups: 'login,nodes,compute,all'
  large:
    aws: 'c4.4xlarge'
    azure: 'Standard_F16s'
    groups: 'login,nodes,compute,all'
  xlarge:
    aws: 'c4.8xlarge'
    azure: 'Standard_F32s'
    groups: 'login,nodes,compute,all'
gpu:
  small:
    aws: 'p3.2xlarge'
    azure: 'Standard_NC6'
    groups: 'login'
  medium:
    aws: 'p3.8xlarge'
    azure: 'Standard_NC12'
    groups: 'login'
  large:
    aws: 'p3.16xlarge'
    azure: 'Standard_NC24'
    groups: 'login'

Interactive Selection

• Very useful for cloud-client usage of modification
• Only show available/allowed instances for node

> flight modify node01
Instance type:
- Compute Tiny (c4.large) <
- Compute Small (c4.xlarge)
- Compute Medium (c4.2xlarge)
- Compute Large (c4.4xlarge)
- Compute Xlarge (c4.8xlarge)