Gce-rescue

New features:

* Skip snapshot creation
* Async backup task (snapshot create)

Patch:
* Handle wrong VM/Zone parsed
* Removed exception when reaching timeout for wait_os_boot
* Regional snapshots. Creation configured to the same region as the disk

Issues:
* 21
* 22
* 23

Notes:
- Fixed absl flags issue that prevent --help to be shown properly.
- Migrated absl to argparse and python native logging.

Initial version.