Simplify test runner by adding a new option '--mayan-apps' that

automatically tests all Mayan apps that report to have tests.
Change the app flag that indicates when an app has test
from 'test' to the more explicit 'has_test'.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/lock_manager/apps.py

@@ -5,6 +5,6 @@ from django.utils.translation import ugettext_lazy as _
 
 
 class LockManagerApp(apps.AppConfig):
+    has_tests = True
     name = 'lock_manager'
-    test = True
     verbose_name = _('Lock manager')