Harden against transiently unavailable backup transports

Summary:
The init & clear operations are particularly important to ensure
delivery when at all possible, so we retry those periodically
if the transport is unavailable when we first attempt them.

Now with 100% less build break.

Bug 11716868

Change-Id: I2af4e93788068cfac97c0a48d3568c561eefa23d

Test Plan: verify restoring with gapps doesnt cause a soft reboot

Reviewers: synergy, jriordan001, raymanfx, donald.munn, rlasalle15, anders3408

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D372