[tests] Fix some issues with maindomain changing sometimes

src/yunohost/tests/test_backuprestore.py

@@ -15,7 +15,7 @@ from yunohost.domain import _get_maindomain
 from moulinette.core import MoulinetteError
 
 # Get main domain
-maindomain = _get_maindomain()
+maindomain = ""
 
 # Instantiate LDAP Authenticator
 AUTH_IDENTIFIER = ('ldap', 'ldap-anonymous')
@@ -24,6 +24,9 @@ auth = None
 
 def setup_function(function):
 
+    global maindomain
+    maindomain = _get_maindomain()
+
     print ""
 
     global auth