Change cp tests that don't specify a Content-Type to check for new binary/octet-stream default instead of server-detected mime type.
Change cp tests that don't specify a Content-Type to check for new
binary/octet-stream default instead of server-detected mime type.

ttiurani/gsutil,dtjackson/gsutil,BrandonY/gsutil,mattdr/gsutil,craigcitro/gsutil,chriskuehl/gsutil-debian,dimfeld/gsutil,fishjord/gsutil,GoogleCloudPlatform/gsutil,GoogleCloudPlatform/gsutil