[tox] Split migractions tests from server environment
These are the longest tests in this environment, so running them apart (in
parallel of others) would hopefully speed up the whole suite.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/html/index.html
Files: /usr/share/doc/cubicweb-documentation/html/*