Add possibility to change k8s images.

* Added possibility to change k8s and netchecker images
from contrail+k8s template.
* Fixed getting node role in virtlet manager.

Change-Id: Ibf281632459136a9f62d1a7f198d27cc488ad67e
Reviewed-on: https://review.gerrithub.io/366394
Reviewed-by: <apanchenko@mirantis.com>
Reviewed-by: Victor Ryzhenkin <vryzhenkin@mirantis.com>
Reviewed-by: Dennis Dmitriev <dis.xcom@gmail.com>
Tested-by: Dennis Dmitriev <dis.xcom@gmail.com>
diff --git a/tcp_tests/managers/virtlet_manager.py b/tcp_tests/managers/virtlet_manager.py
index 2d126e0..717ba76 100644
--- a/tcp_tests/managers/virtlet_manager.py
+++ b/tcp_tests/managers/virtlet_manager.py
@@ -31,7 +31,7 @@
         self.__underlay = underlay
         self.virtlet_nodes = [
             i for i in self.__config.underlay.ssh
-            if ext.UNDERLAY_NODE_ROLES.virtlet_node in i['roles']]
+            if ext.UNDERLAY_NODE_ROLES.k8s_virtlet in i['roles']]
         super(VirtletManager, self).__init__(
             config=config, underlay=underlay)