Exit with code 1 on unknown exceptions when debug flag is enabled
Exit with code 1 on unknown exceptions when debug flag is enabled

This fixes a bug where gsutil would exit with code 0 when
an unknown exception terminated execution and the global debug
(-D) flag was enabled.

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