[migractions] remove any session related leftovers
Also, the migration handler really wants a "repo" session anyway.
This highlights a bug in unittest_wfobjs.test_duplicated_transition
where an old connection is reused. It probably used to work because it
was made of session + set_cnxset magic dust.
Related to #3933480.
/*
* cubicweb js mock for unit tests
* This module defines variables and functions used in quite a few places
* in cw js framework that can't be used or guessed without a real CW server
*/
var pageid = 'my-page-id';
function _(message) {
return message;
}