Rename groupHint to cluster.

Bug: 146460486
Test: atest android.net.IpMemoryStoreTest
Test: atest com.android.server.connectivity.ipmemorystore.IpMemoryStoreServiceTest
Change-Id: I493472cb65262b04769192b702178351416c9869
Merged-In: I805733e201aa1286477cfac589cdf4ac18bb7e2b
(cherry-picked from aosp/1311636)
52 files changed