crimson/os/seastore/seastore_types: introduce base_ertr

crimson/os/seastore/seastore_types: introduce base_ertr

Instead of decalring base_ertr and base_iertr in every file or
class that use them -
* Move base_ertr decleration to the common seastore_types header.
  Note: the price for that is including errorator in seastore_types
        though this seems reasonable considering the benefits.
* Move base_iertr to transaction_interruptor where trans_iertr
  is defined.

Signed-off-by: Matan Breizman <mbreizma@redhat.com>