[server/test] make unittest_migractions.py use new style cubes MigrationTC used old cube layout in cubicweb/server/test/data-migractions/cubes, move them to new style cubes as "cubicweb_<cubename>" in "apphome" (cubicweb/server/test/data-migractions/) which is added to PYTHONPATH by CubicWebTC.

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))