fixing false "boot2docker-vm does not exist."

In case the box is in saved state, its reported as
not existing, I propose introducing a new 'saved'
state for status command

=== sympthom ===
> boot2docker status
[2014-03-27 19:00:35] boot2docker-vm does not exist.

> VBoxManage showvminfo boot2docker-vm|grep State
State:           saved (since 2014-03-27T16:13:24.967000000)
Merge pull request #304 from lalyos/saved-state

fixing false "boot2docker-vm does not exist."