LU-14711 tests: Ensure no eviction with long cache discard

LU-14711 tests: Ensure no eviction with long cache discard

Origin title:

LU-14711 tests: Ensure there's no eviction with long cache discard

Just pause execution while doing page processing
for discard if appropriate failloc is set.

Lustre-change: https://review.whamcloud.com/43869
Lustre-commit: TBD (from 3323b40668cddaa1ac6f6644436bd305c189c5ac)

Change-Id: If0d04f3cad267cbeeab63040d63e048dcf03cd6b
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Test-Parameters: trivial testlist=sanity env=ONLY=903
Reviewed-on: https://review.whamcloud.com/44286
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>