Eliminate deadlock by deferring wipe data call

The call to RecoverySystem.rebootWipeUserData() was made while
holding the lock to DevicePolicyManagerService. But it blocks
waiting for system_process' main thread to receive the ordered
broadcast complete callback. It won't receive that callback
because Keyguard is running on the main thread and is concurrently
blocked on DevicePolicyManagerService.

By moving the call to rebootWipeUserData() out of the synchronized
block the deadlock is eliminated.

Fixes bug 16870054.

Change-Id: I3eb587211e5484859cc9dab7e80e5a1f6c85225d