[AETHER-1299] Implement SPINE pinning policy in SR.

Additionally introduces a new CLI command. Also this review addresses
comments coming from the previous patch [24393] and fixes some issue
seen in the previous patch.

Change-Id: I5362d95ebe1c237eb5bdb13ec34ab109d25f9f7a
diff --git a/impl/src/main/java/org/onosproject/segmentrouting/policy/api/PolicyState.java b/impl/src/main/java/org/onosproject/segmentrouting/policy/api/PolicyState.java
index ad767ec..290852d 100644
--- a/impl/src/main/java/org/onosproject/segmentrouting/policy/api/PolicyState.java
+++ b/impl/src/main/java/org/onosproject/segmentrouting/policy/api/PolicyState.java
@@ -18,6 +18,7 @@
 /**
  * Represents the state of a policy as seen by the system.
  */
+// TODO consider to add a FAILED state for an invalid policy that cannot be fulfilled even after a retry
 public enum PolicyState {
     /**
      * The policy is in the process of being added.