benchmark: use erasure code pool profile

In version > v0.78 the erasure coded pools are configured with a profile (
ceph osd erasure-code-profile ) that is used when creating a new
pool.

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #1 from dachary/wip-erasure-code

benchmark: use erasure code pool profile