LU-11665 tests: check number of pages correctly

LU-11665 tests: check number of pages correctly

On ARM or other 64KB PAGE_SIZE systems, check the read cache size
against the actual PAGE_SIZE instead of just checking the number
of pages being read.

Lustre-change: https://review.whamcloud.com/33772
Lustre-commit: df0bcc96ee578d6661fcc63e82b94e1e569f9efe

Test-Parameters: trivial clientdistro=el8.2 clientarch=aarch64 testlist=sanity

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I8fb90325a18b343c5f5af01df603a25fe33ebbe5
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/40702
Tested-by: jenkins <devops@whamcloud.com>