Log Message:
Update py-google-compute-engine to 20170523 (aka 2.3.7).

May 23, 2017

- Fix account daemon behavior when block-project-ssh-keys is unset in metadata.

April 26, 2017

- Remove logic that overrides home directory permissions.

March 27, 2017

- Prevent unchanged authorized keys file writes.
- Accounts daemon sets the home directory permission to 750 instead of 755.