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.

Test-Parameters: trivial clientarch=aarch64 testlist=sanity
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I8fb90325a18b343c5f5af01df603a25fe33ebbe5
Reviewed-on: https://review.whamcloud.com/33772
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>