Updating sample to utilize Compute Engine API version v1beta14

- Updated API version references to be v1beta14
- Updated URLs pointing to global resources to include '/global' in the
URL path
- Added DEFAULT_ZONE_NAME and updated DEFAULT_ZONE to include it
- Updated DEFAULT_IMAGE to new image name since the old image name
referenced an image resource that has been deprecated
- Updated DEFAULT_MACHINE to use v1beta14 updated URL structure -
'../machineTypes/..'
- Updated compute.operations.list to be compute.global_operations.list
which lists a given project's global operations