brag : meaningfull error messages

To help figure out problems, include the error message in the output
when a submission fails.

Signed-off-by: Loic Dachary <loic@dachary.org>
brag : document the zero argument behavior

Signed-off-by: Loic Dachary <loic@dachary.org>
brag : implement --verbose on client

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #1709 from dachary/wip-brag

brag : useability changes

Reviewed-by: Babu Shanmugam <anbu@enovance.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>