FrameworksServicesTests: allow access to test.sys.boot.reason property

com.android.server.power.PowerManagerServiceTest#testGetLastShutdownReasonInternal due to "RuntimeException: failed to set system property"

W/roidJUnitRunner: type=1400 audit(0.0:6): avc: denied { write } for name="property_service" dev="tmpfs" ino=13178 scontext=u:r:platform_app:s0:c512,c768 tcontext=u:object_r:property_socket:s0 tclass=sock_file permissive=0
W/libc    : Unable to set property "test.sys.boot.reason" to "shutdown,thermal": connection failed; errno=13 (Permission denied)

Had to use precise property definition as com.android.phone accesses
test properties as well.

Test: compile
Bug: 78245377
Change-Id: I2cc810846f8615f2a2fae8e0d4f41de585b7abd7