Add 'adb restore' to parallel 'adb backup'

It won't actually do anything until the 'bu' tool and framework are
updated to respond properly, but this is the adb side of the
necessary infrastructure: we copy the tarfile into the socket pointed
at the device, using the existing mechanisms.

Change-Id: Ic3b5779ade256bd1ad989a94b0685f7b1a7d59d2