Implement 'config get <var>' for the admin socket

Signed-off-by: Wido den Hollander <wido@42on.com>
Fix whitespace indentation

Signed-off-by: Wido den Hollander <wido@42on.com>
Merge pull request #263 from wido/config-get

Add "config get <var>" to the admin 

Reviewed-by: Sage Weil <sage@inktank.com>