Fix terminal handling on Windows

The termios library does not work on Windows. Add a wrapper API to fix
compilation.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
s3_repository: Fix downloading a new image

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Merge pull request #34 from penberg/windows

Fix terminal handling on Windows
Add gce support

Signed-off-by: Asias He <asias@cloudius-systems.com>
ci
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