Allow to specify underlay and salt roles separatelly

- Manage custom node roles with 'underlay' fixture and use the
  nodes names for 'execute_commands' templates:
    export ROLES='["role1", "role2", ...]'

- Install salt-minion on custom node roles from config.underlay.ssh
    export SALT_ROLES='["salt-role1", "salt-role2", ...]'

The SALT_ROLES allows to specify only the nodes for salt-minion, while
other nodes from ROLES will be available only for UnderlayManager.

Change-Id: Iab2d021ecf8a9f2fce6c322aea6439b8d1d11106
diff --git a/tcp_tests/settings_oslo.py b/tcp_tests/settings_oslo.py
index ad4cce3..288013c 100644
--- a/tcp_tests/settings_oslo.py
+++ b/tcp_tests/settings_oslo.py
@@ -129,6 +129,11 @@
     ct.Cfg('templates_dir', ct.String(),
            help="Path to directory with templates",
            default=_default_templates_dir),
+    ct.Cfg('salt_roles', ct.JSONList(),
+           help="Node roles to install salt-minions and manage by salt",
+           default=[ext.UNDERLAY_NODE_ROLES.salt_master,
+                    ext.UNDERLAY_NODE_ROLES.salt_minion,
+                    ext.UNDERLAY_NODE_ROLES.k8s_controller]),
 ]
 salt_opts = [
     ct.Cfg('salt_master_host', ct.IPAddress(),