[server] Handle unique constraint violations under recent sqlite
The error message changed from "columns foo, bar, baz are not unique" to
"UNIQUE constraint failed: table.foo, table.bar, table.baz".
Closes #3564510
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/share/pyshared/cubicweb/skeleton/debian/rules.tmpl)