rgw: bucket index ops on system buckets shouldn't do anything

Fixes: #4508
Backport: bobtail
On certain bucket index operations we didn't check whether
the bucket was a system bucket, which caused the operations
to fail. This triggered an error message on bucket removal
operations.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
mds: CInode::build_backtrace() always incr iter

Always increment the iterator when adding old pools
to the backtrace.  This fixes a bug on files where
the layout had been set to a different pool and then
back to the same pool, causing continuous looping in
the build_backtrace() function.

Fixes #4537.
Signed-off-by: Sam Lang <sam.lang@inktank.com>
Merge pull request #147 from ceph/wip-4537

mds: CInode::build_backtrace() always incr iter

Reviewed-by: Sage Weil <sage@inktank.com>
Merge remote-tracking branch 'gh/next'