mon: make 'ceph osd erasure-code-profile set ...' idempotent

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #1572 from ceph/wip-ec-profile-idempotent

mon: make 'ceph osd erasure-code-profile set ...' idempotent

Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>