erasure-code: create default profile if necessary

http://tracker.ceph.com/issues/8601

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #1966 from dachary/wip-erasure-code-profile-default

DNM: erasure-code: create default profile if necessary

Reviewed-by: Sage Weil <sage@inktank.com>