Feature 10239: Distributed VCA

- Add vca_id in all calls that invoke libjuju. This is for being able to
talk to the default VCA or the VCA associated to the VIM
- Add store.py: Abstraction to talk to the database.
  - DBMongoStore: Use the db from common to talk to the database
  - MotorStore: Use motor, an asynchronous mongodb client to talk to the
database
- Add vca/connection.py: Represents the data needed to connect the VCA
- Add EnvironConfig in config.py: Class to get the environment config,
and avoid LCM from passing that

Change-Id: I28625e0c56ce408114022c83d4b7cacbb649434c
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/n2vc/tests/unit/utils.py b/n2vc/tests/unit/utils.py
index a727072..2f107a7 100644
--- a/n2vc/tests/unit/utils.py
+++ b/n2vc/tests/unit/utils.py
@@ -82,7 +82,18 @@
         detailed_status: str,
         vca_status: str,
         entity_type: str,
+        vca_id: str = None,
     ):
+        """
+        Write application status to database
+
+        :param: db_dict: DB dictionary
+        :param: status: Status of the application
+        :param: detailed_status: Detailed status
+        :param: vca_status: VCA status
+        :param: entity_type: Entity type ("application", "machine, and "action")
+        :param: vca_id: Id of the VCA. If None, the default VCA will be used.
+        """
         self.last_written_values = Dict(
             {
                 "n2vc_status": status,