[virtlet] Refactor virtlet part

- Remove virtlet roles
- Remove virtlet fixtures due virtlet officially installed as
addon if option is enabled
- Move virtlet core test functions under k8smanager.py
- Add show_step into virtlet tests
- Add checks that virtlet is enabled to the beginning of tests

Change-Id: Ibfb499b29727b367afafc68fa13199db13bcccdf
diff --git a/tcp_tests/templates/virtual-mcp11-k8s-calico/underlay.yaml b/tcp_tests/templates/virtual-mcp11-k8s-calico/underlay.yaml
index 658660c..d872f9a 100644
--- a/tcp_tests/templates/virtual-mcp11-k8s-calico/underlay.yaml
+++ b/tcp_tests/templates/virtual-mcp11-k8s-calico/underlay.yaml
@@ -183,7 +183,7 @@
                     - private
 
           - name: {{ HOSTNAME_CTL02 }}
-            role: k8s_virtlet
+            role: salt_minion
             params:
               vcpu: !os_env SLAVE_NODE_CPU, 2
               memory: !os_env SLAVE_NODE_MEMORY, 2048