Treat HTTP code 400 and above as error.

Fixes bug 1116559.

Change-Id: I4b12176599686f7e545b63c8e54cf9da6a1f963e
Fix incomplete sentence in help

`keystone help` only pulls a one line summary from docstrings, so this
summary needed to be condensed.

Change-Id: I9b08c6a8153101b1cc338955078d0d3b6a0aa02e
Merge "Treat HTTP code 400 and above as error."
Merge "Fix incomplete sentence in help"