Handle mailbox update SYNC sms by refreshing mailbox.

Since when a mailbox update (MBU) SYNC message is received it means
something has changed on the server, we need to sync locally. An easy
way to do this is to clear all current messages and reload from the
server.

Bug: 19236241
Change-Id: Ib975098c724e5a34149c50c57ab14c757a3d5cdf
2 files changed