Passing data only through unit relation data

The data between apps should only be passed through
the unit relation data.

The unit tests have also been updated.

Change-Id: Id5467922c3217c84ff1d7bbcdbe7d2a1caba19dd
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/nbi/src/charm.py b/installers/charm/nbi/src/charm.py
index f2b2ecf..848b53d 100755
--- a/installers/charm/nbi/src/charm.py
+++ b/installers/charm/nbi/src/charm.py
@@ -129,10 +129,8 @@
         Args:
             event (EventBase): Kafka relation event.
         """
-        data_loc = event.unit if event.unit else event.app
-
-        message_host = event.relation.data[data_loc].get("host")
-        message_port = event.relation.data[data_loc].get("port")
+        message_host = event.relation.data[event.unit].get("host")
+        message_port = event.relation.data[event.unit].get("port")
 
         if (
             message_host
@@ -162,9 +160,7 @@
         Args:
             event (EventBase): DB relation event.
         """
-        data_loc = event.unit if event.unit else event.app
-
-        database_uri = event.relation.data[data_loc].get("connection_string")
+        database_uri = event.relation.data[event.unit].get("connection_string")
 
         if database_uri and self.state.database_uri != database_uri:
             self.state.database_uri = database_uri
@@ -185,19 +181,17 @@
         Args:
             event (EventBase): Keystone relation event.
         """
-        data_loc = event.unit if event.unit else event.app
-
-        keystone_host = event.relation.data[data_loc].get("host")
-        keystone_port = event.relation.data[data_loc].get("port")
-        keystone_user_domain_name = event.relation.data[data_loc].get(
+        keystone_host = event.relation.data[event.unit].get("host")
+        keystone_port = event.relation.data[event.unit].get("port")
+        keystone_user_domain_name = event.relation.data[event.unit].get(
             "user_domain_name"
         )
-        keystone_project_domain_name = event.relation.data[data_loc].get(
+        keystone_project_domain_name = event.relation.data[event.unit].get(
             "project_domain_name"
         )
-        keystone_username = event.relation.data[data_loc].get("username")
-        keystone_password = event.relation.data[data_loc].get("password")
-        keystone_service = event.relation.data[data_loc].get("service")
+        keystone_username = event.relation.data[event.unit].get("username")
+        keystone_password = event.relation.data[event.unit].get("password")
+        keystone_service = event.relation.data[event.unit].get("service")
 
         if (
             keystone_host
@@ -248,10 +242,8 @@
         Args:
             event (EventBase): Prometheus relation event.
         """
-        data_loc = event.unit if event.unit else event.app
-
-        prometheus_host = event.relation.data[data_loc].get("hostname")
-        prometheus_port = event.relation.data[data_loc].get("port")
+        prometheus_host = event.relation.data[event.unit].get("hostname")
+        prometheus_port = event.relation.data[event.unit].get("port")
 
         if (
             prometheus_host