erasure-code: ruleset-* -> crush-*

erasure-code: ruleset-* -> crush-*

1) ruleset is an obsolete term, and
2) crush-{rule,failure-domain,...} is more descriptive.

Note that we are changing the names of the erasure code profile keys
from ruleset-* to crush-*.  We will update this on upgrade when the
luminous flag is set, but that means that during mon upgrade you cannot
create EC pools that use these fields.

When the upgrade completes (users sets require_osd_release = luminous)
existing ec profiles are updated automatically.

Signed-off-by: Sage Weil <sage@redhat.com>