allow starts N2VCJujuConnector without the parameter api_proxy

Change-Id: I7506f10b89c6837ce019e6db447748de3c811d61
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>
diff --git a/n2vc/n2vc_juju_conn.py b/n2vc/n2vc_juju_conn.py
index ab8c6e8..ed53da4 100644
--- a/n2vc/n2vc_juju_conn.py
+++ b/n2vc/n2vc_juju_conn.py
@@ -175,6 +175,7 @@
             self.warning(
                 "api_proxy is not configured. Support for native charms is disabled"
             )
+            self.api_proxy = None
 
         if "enable_os_upgrade" in vca_config:
             self.enable_os_upgrade = vca_config["enable_os_upgrade"]