CtsLogdTestCases#sepolicy_rate_limiter failure

Cts tests can run in appdomain, which have access to /data/backup/
which leads to zero injection of sepolicy signal to check the logd
and kernel rate limiter.  Switch to /data/drm/ as a better choice
to inject a sepolicy denial either due to dac_override or
dac_read_search because owned by the drm uid and gid, or due to
create sepolicy denial to u:object_r:drm_data_file:s0 to all but
select services.

Test: gTest
Bug: 65843095
Change-Id: I2d72b1407a930c270636a206066d2d15fdec2f77