Reset the error status in the persistent instance

The error state for a resource should not be inherited from the
previous operation to the next time someone grabs the persistant
connection.

Change-Id: I41efc5f448b653300e45cdfacc62a49710a81bf7
Reviewed-on: http://review.couchbase.org/25613
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>