crimson/osd: errorator omap_get_values() ops

crimson/osd: errorator omap_get_values() ops

* os/alienstore: do not panic if retval is less than 0. instead,
  translate ENOENT to enoent and other erros to input_output_error
* os/FuturizedStore: errorator omap_get_values() variants, so
  they return errorator::future<> instead of plain seastar::future<>
* os/seastore: update accordingly.
* osd/pg_backend: use enodata for OI without omap in it. better
  performance, and better readability this way.

Signed-off-by: Kefu Chai <kchai@redhat.com>