user can specify 'rgw port' to listen on a tcp port.
'rgw socket path' overrides 'rgw port'.
An 'rgw host' can be set to listen on a specific ip (default is 0.0.0.0)

Signed-off-by: Guilhem Lettron <guilhem.lettron@youscribe.com>
Merge pull request #46 from Youscribe/rgw_bind

rgw: #4072 listen on tcp

Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>