txn: fix on_rollback trigger args for txns aborted by yield/timeout

Currently, if a transaction is aborted by a fiber yield or by a timeout,
txn_rollback_to_svp() is called to rollback all statements of the txn.
After that the transaction is completely aborted on attempt to commit it.
If an on_rollback trigger is set, it is called from txn_complete_fail(),
however it receives an empty iterator, because at this point the statements
are already destroyed. This patch invokes on_rollback triggers directly
from txn_rollback_to_svp() for abort-by-yield, and postpones the rollback
for abort-by-timeout.

Closes #9340

NO_DOC=bugfix