objectpool: Fix error code when trying to recreate existing pool
With the recent refactorings to create object pools atomically the error
code has changed when the target exists from FailedPrecondition
to
AlreadyExists
. While the latter is arguably better, Rails' rspecs
still expect the former error code.
Fix this by overriding the error code so that for the time being we
abide and use whatever Rails wants to see. Eventually though we should
fix this to return AlreadyExists
so that we're consistent with all the
other repository-creating functions.
Changelog: fixed