Finalize MEP functionality.

1) Finish plumbing of PULLING_CALL state.
2) Add new disconnect cause used when maximum number of calls across
all devices has been reached.
3) Add PII mask for toString of ImsExternalCallState.

Bug: 29522023
Change-Id: I78a0a9f3c3d846cfc58a1c5bcc6f105027602cbc

telecomm/java/android/telecom/ConnectionService.java

@@ -556,6 +556,9 @@ public abstract class ConnectionService extends Service {
                 case Connection.STATE_DIALING:
                     mAdapter.setDialing(id);
                     break;
+                case Connection.STATE_PULLING_CALL:
+                    mAdapter.setPulling(id);
+                    break;
                 case Connection.STATE_DISCONNECTED:
                     // Handled in onDisconnected()
                     break;