erasure-code: ErasureCodeShec update default values to string

erasure-code: ErasureCodeShec update default values to string

Update the ErasureCodeShec::init function to use string default
values. The default profile values for technique, ruleset-root and
ruleset-failure-domain are set for the user to see.

The error message when an invalid technique is provided is written to
the error stream to be returned to the user instead of being written to
the OSD log.

Updating other values from the profile would require deeper changes and
is left for later.

http://tracker.ceph.com/issues/9589 Fixes: #9589

Signed-off-by: Loic Dachary <ldachary@redhat.com>