[FIX] web,*: fix race condition with m2o quick create

*sale,sale_product_configurator

Let's assume a form view containing a many2one with an onchange
that updates the value of a one2many. Do a quick create in the
many2one. While the name_create request is pending, add a row to
the one2many but do not leave it. When the name_create returns, and
the onchange has been performed, the one2many is reset, and the row
is no longer in edition (worse, it could be invalid, i.e. in a state
that the user could not have reached in a normal situation).

This commit fixes this issue by considering the whole [name_create +
onchange] operation as one. This operation is executed in the mutex
of the model, so the other request (adding a row to the one2many) is
delayed until the many2one value has been correctly set.

This fixes an issue with the sale and rental tours (on sale_order),
that had been deactivated for a while.