os/FileStore: fix ENOENT error code for getattrs()

In commit dc0dfb9e01d593afdd430ca776cf4da2c2240a20 the omap xattrs code
moved up a block and r was no longer local to the block.  Translate
ENOENT -> 0 to compensate.

Fix the same error in _rmattrs().

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Greg Farnum <greg@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: copy: use aggregate return code instead of individual Op return

It appears that the OSD is not filling in the individual return codes, and they
should be equivalent for all purposes we care about here (the only Op we are
doing is the copy-get, and if it fails we are getting its failure code).

Reported-by: Sage Weil <sage@inktank.com>
Signed-off-by: Greg Farnum <greg@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>