Rework radosgw keys and data dir path

Rework radosgw keys and data dir path

Fix the usage of Upstart for Ubuntu machines instead of the init.d
script.
Note that because of the way upstart init script looks at the radosgw id
the command 'start radosgw id=' is broken, you should use 'start
radosgw-all' instead.
Keep backard compatibility with the radosgw init script as well by using
client prefixed by 'client.radosgw'.

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>