Add check_for_ufs.sh script

When run as root on an Android device, this script "succeeds" (exit
code of 0) if UFS is being used for userdata on the device.  It gives
a non-zero exit code otherwise.

UFS has substantially better performance than eMMC in terms of
both raw throughput, and cases like performing reads while writing
back to disk.

For this reason, some future test suites will start checking whether
devices are using UFS or eMMC.  There is no simple property to check
for UFS vs. eMMC, so we need some logic which this script implements.
While future test suite changes will be across different areas, we
want this specific logic centrally located within AOSP code so all
implementations are the same and any bugs can be centrally fixed.

Bug: 409357709
Test: Run across a couple different devices with UFS and eMMC
Flag: EXEMPT for standalone script
Change-Id: I27461cd7d98a0a4e138d662aed6a0796af3cf362