check for VM in virtualbox; add stub for coverage

Signed-off-by: Evan Hazlett <ejhazlett@gmail.com>

README.md

@@ -128,11 +128,13 @@ BATS (use that link).  Then run `./script/build` to generate the binary.  Once
 you have the binary, you can run test against a specified driver:
 
 ```
-$ DRIVER=virtualbox bats test/driver.bats
+$ bats test/driver-virtualbox.bats
  ✓ virtualbox: machine should not exist
+ ✓ virtualbox: VM should not exist
  ✓ virtualbox: create
  ✓ virtualbox: active
  ✓ virtualbox: ls
+ ✓ virtualbox: run busybox container 
  ✓ virtualbox: url
  ✓ virtualbox: ip
  ✓ virtualbox: ssh
@@ -144,6 +146,7 @@ $ DRIVER=virtualbox bats test/driver.bats
  ✓ virtualbox: machine should show running after restart
  ✓ virtualbox: remove
  ✓ virtualbox: machine should not exist
+ ✓ virtualbox: VM should not exist
 
 15 tests, 0 failures
 ```

test/driver-virtualbox.bats

@@ -16,6 +16,11 @@ function setup() {
   [ "$status" -eq 1  ]
 }
 
+@test "$DRIVER: VM should not exist" {
+  run VBoxManage showvminfo $NAME
+  [ "$status" -eq 1  ]
+}
+
 @test "$DRIVER: create" {
   run machine create -d $DRIVER $NAME
   [ "$status" -eq 0  ]
@@ -109,6 +114,11 @@ function setup() {
   [ "$status" -eq 1  ]
 }
 
+@test "$DRIVER: VM should not exist" {
+  run VBoxManage showvminfo $NAME
+  [ "$status" -eq 1  ]
+}
+
 @test "$DRIVER: cleanup" {
   run rm -rf $MACHINE_STORAGE_PATH
   [ "$status" -eq 0  ]

test/test.go

@@ -0,0 +1,2 @@
+// stub for coverage
+package test