Reworked pause/save/suspend/resume logic. pause really pauses, save really saves, catch when a VM really doesn't exist vs. fell-through because of state-change

Fixes for a few things that dent **LeastSurprise** that are related to, but separate from [767e69e](https://github.com/boot2docker/boot2docker/commit/767e69e03ec05b28680f569ba7806ad28acc0b6a) 

```
is_suspended() {
    info | grep -E "State:[ ]+suspended" > /dev/null
}
```
for example won't ever match because "suspended" isn't a valid VBoxManage state keyword, "paused" is.  
Also, If a VM is in the middle of a state change and someone runs
```
boot2docker status
```
 like right after calling 
```
boot2docker save
```
 , you can get back "vm does not exist" until the operation completes in the background a minute or two later.