erasure-code: override the default only if the plugin match

erasure-code: override the default only if the plugin match

When setting a new erasure coded profile, the key/value of the default
profile are re-used so that ruleset-failure-domain=osd can be overridden
like so:

        ceph osd erasure-code-profile set ruleset-failure-domain=osd

This is however not appropriate if the plugin is different from the
defaut plugin (for instance LRC instead of jerasure) because the
parameters are not the same.

If the plugin is changed, the default profile is not reused.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>