Add a configurable to allow bucket perms to be checked before key perms
through rgw_defer_to_bucket_acls config option.  This configurable defaults
to an empty string.  Option values include:

  - recurse: If requesting perm PERM on a key, allow if user has
    PERM on the
    bucket to which the key belongs.

  - full_control: If requesting perm PERM on a key, allow if user
    has
    FULL_CONTROL on the bucket to which the key belongs.

This allows users to give someone full bucket perms and be able to
operate on the keys in the bucket without modifying the perms of every
key in the bucket.  This breaks S3 compatability, but that's why
it's a configurable!

Signed-off-by: Liam Monahan <liam@umiacs.umd.edu>
Merge pull request #672 from liammonahan/wip-defer-to-bucket-acls

Add a configurable to allow bucket perms to be checked before key perms

Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>