[gce] Disk image capture is a global, not zone operation
[gce] Disk image capture is a global, not zone operation

Bug: skia:7278
Change-Id: Id95278674b955887fb7129056df227fea9ea3c4c
Reviewed-on: https://skia-review.googlesource.com/71141
Reviewed-by: Stephan Altmueller <43343ec95731c0e8daa7359daf7f2f3935582b24@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot