Add a oneshot init service, to be triggered early in the boot.
This is unlikely to be the permanent solution, but allows us
to get off the ground by at least getting the prop set.
Bug: 137191822
Test: m com.android.sdkext
Test: boot && adb shell getprop | grep sdk_info
Change-Id: I253c56961289d1226f3a9a471e7b6ca047c52a4e
Put the lowest seen number in a persist sysprop.
Bug: 137191822
Test: manual ran derive_sdk on device with fake protos installed
Change-Id: Ic73d615d9d60769d237aa5a72dae2dfe56463007