cubicweb #1009317 create_eid can deadlock [resolved]

When not using PostgreSQL (for which a SEQUENCE is used), create entity can deadlock (because the UPDATE will lock the underlying table until transaction is committed, but another thread can take the Python Lock object and get stuck afterwards by the DB thread).

This concerns all instances running on a db backend other than PG.

done in3.8.3
load left0.000
closed by<not specified>