[server/test] use server config in migration
This allows a lighter initialisation (no rtag needed).
Execution of those test move from 300 secondes to 220 seconds here. A 25%
speedup
if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
ask_confirm=False):
rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
ask_confirm=False)