rgw: forward delete_bucket to master region

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: verify bucket location only if exists

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: Do not assum rest connection to be established

Added a check to verify that rest connection is correctly initialized,
preventing a segmentation fault.

Signed-off-by: Christophe Courtaut <christophe.courtaut@gmail.com>
Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>