ProcessPendingMessagesAction works based on subscriptions

PorcessPendingMessagesAction queues one message for sending/downloading
associated with a subscription triggering current action at a time. And
the ConnectivityUtil also works based on subscriptions so that pending
messages can be processed regardless of other phones' state in multi-sim
case.

It includes cleanup code as well.

Test: Manual

Change-Id: Id6b4f4a0aa6a3291e7a4d8a5d3f0fbb9db3c5b86
Signed-off-by: Taesu Lee <taesu82.lee@samsung.com>

src/com/android/messaging/util/BuglePrefsKeys.java

@@ -66,6 +66,6 @@ public final class BuglePrefsKeys {
      * The attempt number when retrying ProcessPendingMessagesAction
      */
     public static final String PROCESS_PENDING_MESSAGES_RETRY_COUNT
-            = "process_pending_retry";
+            = BuglePrefs.SHARED_PREFERENCES_PER_SUBSCRIPTION_PREFIX + "process_pending_retry";
 
 }