Upgrade the image - preserving machine state

Stop the VM, download, and restart (preserve machine state - ie if it was running before, it will be running after upgraded).

Docker-DCO-1.1-Signed-off-by: Michael Neale michael.neale@gmail.com (github: michaelneale)
https://github.com/boot2docker/boot2docker-cli/pull/193.patch
```patch
diff --git a/.gitignore b/.gitignore
index 2d18d02..45d168d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,4 @@ nbproject
 *.sublime-project
 *.sublime-workspace
 *.swp
+boot2docker-cli
\ No newline at end of file
```