update_engine_common: allow BLKROGET and BLKROSET

Allow BLKROGET and BLKROSET on the block devices underlying the /system
and rootfs partitions. As part of the Android boot process, the system
sets the block devices read-only to prevent accidental modification to
these partitions. Update engine needs the ability to adjust the block
device read-only flag in order to apply updates.

Addresses the following denials:

update_engine: type=1400 audit(0.0:96): avc: denied { ioctl } for path="/dev/block/sda33" dev="tmpfs" ino=15369 ioctlcmd=125e scontext=u:r:update_engine:s0 tcontext=u:object_r:system_block_device:s0 tclass=blk_file permissive=0
update_engine: type=1400 audit(0.0:97): avc: denied { ioctl } for path="/dev/block/sda33" dev="tmpfs" ino=15369 ioctlcmd=125d scontext=u:r:update_engine:s0 tcontext=u:object_r:system_block_device:s0 tclass=blk_file permissive=0

Test: policy compiles
Bug: 118150702
Change-Id: I65a3d041b6d6b7955bcd901637a543524fc34a06