STT: Get disk size data from the stt build test

Get the size of build artifacts using df.
It collect the amount of disk space used for build for all targets.

Bug: 302075773
Test: combined_build_test.sh -t <target> -v userdebug \
            -a <alter_target> -o -c droid
Change-Id: I4c59bc181164f4e8e13277719dc16158d3814f49
1 file changed