sshclient: Fix the iteration through the environment

Change-Id: I53e54561ec9ce8a999bac0fcf8451e3462352402
diff --git a/mdt/sshclient.py b/mdt/sshclient.py
index f12ca77..8942081 100644
--- a/mdt/sshclient.py
+++ b/mdt/sshclient.py
@@ -163,7 +163,7 @@
     def _generateEnvironment(self):
         environment = {}
         for pattern in self.envWhitelist.split(' '):
-            for name, value in os.environ.keys():
+            for name, value in os.environ.items():
                 if fnmatch.fnmatch(name, pattern):
                     environment[name] = value
         return environment