[FIX] mail: tests: move utils in correct bundle
[FIX] mail: tests: move utils in correct bundle

Those test utils files should be in the test assets bundle such
that they are available for potential other test suites (e.g. the
new im_support suite).

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo