reupload: libsnapshot: set thread priority

It looks like we can't use <uint> as type with specifying size

Read merge thread + worker thread priority from build configurations. In
the case of low memory devices, a lower priority will reduce CPU
utilization post OTA reboot.

Test: th
Change-Id: Ie895be32e3aea66b46503c5270939bb42f58494a
2 files changed