Report list of devices in the REST API

[cfergeau]

The aim of this PR was to add the list of devices to the /inspect endpoint with their parameters.
This supersedes #73

My initial goal was to only add tests for this code.
Along the way I found 2 related issues (memory byte/MiB confusion, and too long unix socket paths) which I fixed, and I also realized the code from #73 could be made simpler: config.VirtualMachine already can be serialized to/from json, so we don't need any new code.

[BlackHole1]

LGTM

[openshift-ci]

@BlackHole1: changing LGTM is restricted to collaborators

In response to this:

LGTM

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[cfergeau]

This can be tested by starting vfkit with --restful-uri unix:///Users/teuf/dev/vfkit/rest.sock and then running curl --unix-socket /Users/teuf/dev/vfkit/rest.sock http://unused/vm/inspect

[praveenkumar]

Tested with following and works as expected

✗ ./out/vfkit \
    --cpus 2 --memory 2048 \
    --bootloader efi,variable-store=efi-variable-store,create \
    --device virtio-blk,path=vfkit-test-image.raw \
>   --restful-uri unix:///Users/prkumar/dev/vfkit/rest.sock
INFO[0000] &{2 2048    {[efi variable-store=efi-variable-store create] true}  [virtio-blk,path=vfkit-test-image.raw] unix:///Users/prkumar/dev/vfkit/rest.sock  false} 
INFO[0000] boot parameters: &{EFIVariableStorePath:efi-variable-store CreateVariableStore:true} 
INFO[0000]                                              
INFO[0000] virtual machine parameters:                  
INFO[0000] 	vCPUs: 2                                    
INFO[0000] 	memory: 2048 MiB                            
INFO[0000]                                              
INFO[0000] Adding virtio-blk device (imagePath: vfkit-test-image.raw) 
INFO[0000] virtual machine is running                   
INFO[0000] waiting for VM to stop    

and api response

✗ curl --unix-socket /Users/prkumar/dev/vfkit/rest.sock http://unused/vm/inspect | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   236  100   236    0     0   524k      0 --:--:-- --:--:-- --:--:--  230k
{
  "vcpus": 2,
  "memoryBytes": 2147483648,
  "bootloader": {
    "kind": "efiBootloader",
    "efiVariableStorePath": "efi-variable-store",
    "createVariableStore": true
  },
  "devices": [
    {
      "kind": "virtioblk",
      "devName": "virtio-blk",
      "imagePath": "vfkit-test-image.raw"
    }
  ]
}

/lgtm

[praveenkumar]

/approve
/lgtm

[openshift-ci]

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This pull-request has been approved by: BlackHole1, praveenkumar
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