ceph-objectstore-tool: Clean up error handling

ceph-objectstore-tool: Clean up error handling

Use negative errors throughout and positive error to specify exit status
cpp_strerror() handles negative errors
Clean up main() code to use local "ret"
Let end of main() decide how to treat the final value of "ret"

Signed-off-by: David Zafman <dzafman@redhat.com>
(cherry picked from commit a50679a1a3313e4090bf24f6e4dda28e7d67d731)

Adjust back cherry-pick f237ed97228839a1b412ad213945f0343df05bf5
    Switched to use ret as in the original change from master