Disabling a plugin with non-active applications leaves those applications in teminated lost state

[Tianqi Xiao]

An error occurred during enabling heat plugin in my sunbeam cloud, causing heat related applications to stuck in `waiting` state. So I decide to disable the plugin to remove those applications. The output of from sunbeam shows no error:
```
ubuntu@sunbeam:~$ sunbeam disable heat
OpenStack heat application disabled.
```
but the removal is actually incomplete, leaving those applications in `terminated lost` state:
```
heat-cfn-mysql-router/0 terminated lost 10.1.232.63 unit stopped by the cloud
heat-cfn/0 terminated lost 10.1.232.14 unit stopped by the cloud
heat-mysql-router/0 terminated lost 10.1.232.62 unit stopped by the cloud
heat/0 terminated lost 10.1.232.2 unit stopped by the cloud
```

The problem is like due to provider removing application without `--force` flag, but I think Sunbeam should at least provide an info or warning message when those applications are not fully cleaned.