Fix KeyError in exception message of manager

This resolves the KeyError getting written to the logs instead of
the actual exception message.

Change-Id: Ia1600a6990568f2bf5a8d8a38de35a5d3b182931
Closes-Bug: #1541922
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 72424ad..1962286 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -377,7 +377,7 @@
             linux_client.validate_authentication()
         except Exception as e:
             message = ('Initializing SSH connection to %(ip)s failed. '
-                       'Error: %(error)s' % {'ip_address': ip_address,
+                       'Error: %(error)s' % {'ip': ip_address,
                                              'error': e})
             caller = misc_utils.find_test_caller()
             if caller: