After microbosh deleted; allow it to be redeployed

Currently, we get an error like:

```
uploading /tmp/remote_script_deploy_micro_bosh to Inception VM
Deployment set to '/var/vcap/store/microboshes/deployments/microbosh-aws-us-east-1/micro_bosh.yml'
Downloaded stemcell path /var/vcap/store/stemcells/micro-bosh-stemcell-aws-0.8.1.tgz
Performing update deploy to micro BOSH microbosh-aws-us-east-1
No existing instance to update
       error  deploy micro bosh
Failed to complete Stage 5: Deploying micro BOSH
```

This is because it is not intelligently looking into bosh-deployments.yml to see if it is in fact running.

When a deployment has been deleted, this yml looks like:

``` yaml
# cat bosh-deployments.yml 
--- 
instances: 
- :id: 1
  :name: microbosh-aws-us-east-1
  :uuid: bm-096bc437-b531-4260-a57f-8ea54db2f8d2
  :stemcell_cid: 
  :stemcell_name: 
  :vm_cid: 
  :disk_cid: 
disks: []

aws_instances: []
```