updog changes to support the Update API

[etungsten]

Issue number: #942 (comment) and #942 (comment)

Description of changes:

Author: Erikson Tung <etung@amazon.com>
Date:   Wed Jun 17 11:04:03 2020 -0700

    updog: new subcommand to revert 'update-apply'
    
    Adds a new subcommand for reverting actions done by 'update-apply'.
    Used to "deactivate" an update.

Author: Erikson Tung <etung@amazon.com>
Date:   Wed Jun 17 10:52:25 2020 -0700

    updog: use version-lock and ignore-wave setting for default behavior
    
    updog reads the 'version-lock' and 'ignore-wave' settings for
    determining default update behavior. Still allows overrides via the
    command line options.

Author: Erikson Tung <etung@amazon.com>
Date:   Mon Jun 8 14:33:16 2020 -0700

    settings: add new 'version-lock' and 'ignore-waves' settings
    
    Adds a 'version-lock' setting for specifying the version to update to
    when updating.
    
    Adds a 'ignore-waves' setting for specifying whether to respect update
    waves when updating.

Author: Erikson Tung <etung@amazon.com>
Date:   Mon Jun 8 14:30:21 2020 -0700

    models: new 'FriendlyVersion' model type
    
    Adds a new model type to represent versions that can optionally be
    prefixed with 'v' or represeted by "latest"

Testing done:
Build an image with release version set to 0.3.2, launched instance where version-lock is set to 0.3.3. Then tried the following:

Updog configuration generated properly.

bash-5.0# cat /etc/updog.toml 
metadata_base_url = "https://updates.bottlerocket.aws/2020-02-02/aws-k8s-1.15/x86_64/"
targets_base_url = "https://updates.bottlerocket.aws/targets/"
seed = 191
version_lock = "v0.3.3"
ignore_waves = false
bash-5.0# cat /etc/os-release 
NAME=Bottlerocket
ID=bottlerocket
PRETTY_NAME="Bottlerocket OS 0.3.2"
VARIANT_ID=aws-k8s-1.15
VERSION_ID=0.3.2
BUILD_ID=7192d50a-dirty

Initiate update with updog update-image and see that by default, updog updates to the version-locked version (0.3.3 in this case).

bash-5.0# updog whats      
aws-k8s-1.15 0.3.3
bash-5.0# updog whats --all
aws-k8s-1.15 0.3.4
aws-k8s-1.15 0.3.3
aws-k8s-1.15 0.3.2
aws-k8s-1.15 0.3.1
aws-k8s-1.15 0.3.0
bash-5.0# updog update-image  
Starting update to 0.3.3
Update applied: aws-k8s-1.15 0.3.3

I could also update the boot flags and then revert it via updog revert-update-apply

bash-5.0# updog update-apply
bash-5.0# signpost status
OS disk: /dev/nvme0n1
Set A:   boot=/dev/nvme0n1p2 root=/dev/nvme0n1p3 hash=/dev/nvme0n1p4 priority=1 tries_left=0 successful=true
Set B:   boot=/dev/nvme0n1p6 root=/dev/nvme0n1p7 hash=/dev/nvme0n1p8 priority=2 tries_left=1 successful=false
Active:  Set A
Next:    Set B

bash-5.0# updog revert-update-apply   
bash-5.0# signpost status          
OS disk: /dev/nvme0n1
Set A:   boot=/dev/nvme0n1p2 root=/dev/nvme0n1p3 hash=/dev/nvme0n1p4 priority=2 tries_left=0 successful=true
Set B:   boot=/dev/nvme0n1p6 root=/dev/nvme0n1p7 hash=/dev/nvme0n1p8 priority=0 tries_left=1 successful=false
Active:  Set A
Next:    Set A

bash-5.0# updog update-apply       
bash-5.0# signpost status   
OS disk: /dev/nvme0n1
Set A:   boot=/dev/nvme0n1p2 root=/dev/nvme0n1p3 hash=/dev/nvme0n1p4 priority=1 tries_left=0 successful=true
Set B:   boot=/dev/nvme0n1p6 root=/dev/nvme0n1p7 hash=/dev/nvme0n1p8 priority=2 tries_left=1 successful=false
Active:  Set A
Next:    Set B
bash-5.0# 

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[etungsten]

Push above fixes the unit tests that were failing due to the newly added fields.

[etungsten]

Merged these changes into the update API PR (#942), closing.