Add 'state' field to interfaces and sub-interfaces

Assert that children cannot be 'up' of their parent is 'down'. Add tests. Update user-guide.

unittest/test_interface.yaml

@@ -10,9 +10,9 @@ interfaces:
         description: "This sub-int is invalid because it has no outer dot1q and dot1ad"
         encapsulation:
           inner-dot1q: 1000
-
       102:
         description: "This sub-int is has the same encap as 103"
+        state: down
       103:
         description: "This sub-int is has the same encap as 102"
         encapsulation:
@@ -59,6 +59,7 @@ interfaces:
   GigabitEthernet2/0/0:
     description: "This interface has no sub-ints"
     lcp: "e2"
+    state: down
 
   GigabitEthernet3/0/0:
     l2xc: GigabitEthernet3/0/1

unittest/yaml/error-subinterface9.yaml

@@ -0,0 +1,17 @@
+test:
+  description: "A sub-interface cannot be up if its parent is down."
+  errors:
+    expected:
+     - "sub-interface .* cannot be up if parent .* is down"
+    count: 1
+---
+interfaces:
+  GigabitEthernet1/0/0:
+    state: down
+    lcp: "e1"
+    sub-interfaces:
+      100:
+        state: up
+        encapsulation:
+          dot1q: 100
+          exact-match: false