Fix imports for tests

[Ragzouken]

nanover-core has an __init__.py which seems necessary for the relative imports it uses, but this occupies tests in the namespace so no other set of tests can have an __init__.py -- what can be done to make this work properly?

[jbarnoud]

The simplest solution is maybe to give distinct names to each test directories. This would avoid one type of unnecessary coupling between the test suites.