Add a test to check spurious database connections
The problem occurs when migrating from postgresql 9.1 to 9.4 which occurs when migrating from wheezy to jessie. The chosen behavior is :
- stop xivo services
- check presence of unexpected active DB connections
- if no: stop the remainig services and continue the upgrade
- if yes: abort the upgrade and display an warning for the admin to urge him to stop these unexpected connections
The check was added in the exec_wheezy_to_jessie_migration function.
Closes #399