Clarify that global -o option does not work with integration tests
Clarify that global -o option does not work with integration tests

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