rgw: making implicit_tenants backwards compatible.

rgw: making implicit_tenants backwards compatible.

In jewel, "rgw keystone implicit tenants" only applied to swift. As of
luminous), this option applies to s3 also.
Sites that used this feature with jewel now have outstanding data that
depends on the old behavior.

The fix here is to expand "rgw keystone implicit tenants" so that it
can be set to any of "none", "all", "s3" or "swift" (also 0=false=none,
1=true=all).  When set to "s3" or "swift", the actual id lookup
is also partitioned.

Formerly "rgw keystone implicit tenants" was a legacy opt.
This change converts it to the new style of option,
including support for dynamically changing it.

Fixes: http://tracker.ceph.com/issues/24348
Signed-off-by: Marcus Watts <mwatts@redhat.com>