Fixes to demo run script (again).
Remove the dependency on the Files API by using GoogleCloudStorageOutputWriter instead of BlobstoreOutputWriter (as BlobstoreOutputWriter depends on the Files API.)
There is no BlobstoreZipInputReader equivalent in GCS. However as the BlobstoreZipInputReader does not use the Files API, we can continue to use this reader even after the Files API is turned-off completely.
(We will leave it up to the open source community to implement a similar reader based on GCS.)

R=tkaitchuck
DELTA=34 (21 added, 0 deleted, 13 changed)

Revision created by MOE tool push_codebase.
MOE_MIGRATION=7205