More robust P4Runtime group handling

This patch solves the PENDING_UPDATE and PENDING_ADD_RETRY issue
observed on the ONS EU topology.

The P4Runtime action profile group handling has been re-implemented to
be robust against inconsistencies of the device mirror, which is now
periodically synchronized with the device state. Similarly, we implement
a routine in the P4RuntimeClient to cleanup unused action profile
members.

This patch includes also:
-  Refactor PI handle classes to allow creating handles without the
entity instance
- Use list instead of collections in P4RuntimeClient methods, as order
of updates sent and/or entities received from the device is important

Change-Id: I2e7964ce90f43d66680131b47ab52aca32ab55d2
diff --git a/core/net/src/test/java/org/onosproject/net/pi/impl/PiGroupTranslatorImplTest.java b/core/net/src/test/java/org/onosproject/net/pi/impl/PiGroupTranslatorImplTest.java
index aeaa553..6c86604 100644
--- a/core/net/src/test/java/org/onosproject/net/pi/impl/PiGroupTranslatorImplTest.java
+++ b/core/net/src/test/java/org/onosproject/net/pi/impl/PiGroupTranslatorImplTest.java
@@ -109,6 +109,7 @@
                 .withId(ACT_SET_EGRESS_PORT_WCMP_ID)
                 .withParameter(param).build();
         return PiActionGroupMember.builder()
+                .forActionProfile(ACT_PRF_WCMP_SELECTOR_ID)
                 .withAction(piAction)
                 .withId(PiActionGroupMemberId.of(BASE_MEM_ID + portNum))
                 .withWeight(DEFAULT_MEMBER_WEIGHT)